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An observer uses Continuous Clocking Science Mode to acquire, process and telemeter high time-resolution, 1-dimensional images from the CCD array. An observer uses a Continuous Clocking Parameter Block to configure a Continuous Clocking Science Run, and "Start Continuous Clocking Run" and "Stop Continuous Clocking Run" commands to start and stop the run.
Continuous Clocking Science Mode provides data as a time-series of events which occurred along the columns of a CCD. An analogy is that of a strip-chart recorder, where each CCD column acts as a single pen.
To execute a Continuous Clocking Science Run, an observer sends a "Start Continuous Clocking Run" command to ACIS. ACIS retrieves the parameter block referenced by the start command, dumps the parameter block(s), and proceeds to execute the science run, optionally computing and sending the CCD bias values, and then processing the event data in blocks of 512 rows. Although each block of 512 rows is processed as a unit, there is no additional time delay between row 511 of one block, and row 0 of the next. If telemetry stream or the processor become saturated, data is discarded in units of 512 rows until the condition subsides. The observer allows ACIS to acquire, process and telemeter CCD data for a period of time, after which the observer sends a "Stop Continuous Run" command to ACIS. ACIS then stops the run and telemeters a Science Run Report. Optionally, the observer may then decide to recompute the bias values and send a "Compute Continuous-Clocking Bias" command. ACIS will then re-compute and telemeter the bias values and then stop.
If the observer requires parameters not already provided by the ACIS parameter library, the observer must issue a "Load Continuous Clocking Parameter Block" command to load the desired parameters for the run. If the loaded parameter block requires custom event processing windows, the observer must also issue a "Load 1-D Window List" command to place the desired window settings into the instrument.
An observer configures Continuous Clocking Mode using a Continuous Clocking Mode Parameter Block. Table 27 describes the content of a Continuous Clocking Parameter Block.
TABLE 27. Continuous Clocking Parameter Block (Continued)
------------------------------------------------------------------------------------------------------------ Req Item Description------------------------------------------------------------------------------------------------------------ 27-1 Parameter Block Iden This item is a ground-supplied identifier which is echoed by the tifier instrument software in key portions of the science telemetry. 27-2 FEP CCD Selection These items specify which CCD a given FEP should process. The items are indexed by FEP Id. Any given CCD may be specified more than once in the set, at the cost of reducing the total number of CCDs being used. CCDs or FEPs which are not powered on (see Section 3.2.7 on page 99) are ignored and will not be used for the run. If there are no powered CCD being processed by a powered FEP, the science run will be aborted. 27-3 Number of Rows to This specifies the number of rows to sum prior to clocking out the Sum output registers, expressed in powers of 2. For example, 0 means don't perform any row summation, 1 means sum 2 rows, 2 means sum 4 rows, etc. This value can range from 0 to 9 (i.e. sum a maxi mum of 512 rows) (NOTE: Power constraints may further restrict the total number of rows that can be summed. Such restrictions, however, do not have to be built into the instrument software). 27-4 Number of Columns to This specifies the number of pixels to sum at the Output Node prior Sum to each transfer to the DPA, expressed in powers of 2. For example, 0 means don't perform any column summation, 1 means sum 2 col umns, 2 means sum 4 columns, etc. This value can range from 0 to 6 (i.e. sum a maximum of 64 columns to ensure that each quadrant contain at least 4 columns). 27-5 Output Register This item controls the clocking mode of all of the CCD's Serial Out Clocking Mode put Shift Registers. This item can specify either Full-Mode, AC- Mode, BD-Mode or Diagnostic-Mode. See Section 2.2.2 on page 20 for a description of these modes. 27-6 Number of Overclock This item specifies the number of extra summed pixel pairs to clock Pairs out of the Serial Output Shift Registers. Continuous Clocking Mode uses these pixel sums to determine the bias introduced in the CCD's pixel pulse height by the analog electronics. This value can range from 0 to 15 pairs of pixels. 27-7 Video Chain This item controls the response of the Video Subsection in the Detec Responses tor Electronics Assembly. This item selects 1 or 4 electrons per Ana log-to-Digital Unit (ADU). These items are indexed by FEP Id. If a single CCD is specified by more than 1 FEP entry, then the last cor responding chain response entry is used for the listed CCD. 27-8 Reference to an This is an optional item which allows a maintainer to by-pass the on- explicit DEA Load board SRAM/PRAM load builder, and load these areas directly. This reference points directly into BEP memory. If 0, then no explicit DEA load is to be used. If not 0, then the item points to the memory block which contains the load image to use. Post-launch DEA load images are uplinked into memory by the maintainer using the Write Memory function of the instrument (see Section 3.2.8.3.2 on page 108), or via a patch. This parameter is intended to be used by the maintainer of the instrument, and should be 0 during normal operations. The format of the referenced SRAM/PRAM load will be specified in the ACIS Instrument Software Detailed Design Specifi cation (AS-BUILT), MIT 36-53200, and shall support different load contents for distinct DEA boards. 27-9 Front End Selection This item specifies whether or not the Front End Processor should Algorithm supply all pixels to the Back End (Raw Mode), or only those whose center is above the current threshold and whose pulse height is greater than or equal to the (possibly summed) pixel to its left, and greater than the (possibly summed) pixel to its right (Event-finding Mode). 27-10 Threshold Set Points These items control the minimum pulse-height above bias a pixel sum should have to be considered an event candidate. Each of these items applies to a specific CCD output node. These values can range from -4096 to 4095. These values are only used when the Front End Selection Algorithm is in Event-finding Mode. One set of four val ues is specified for each FEP. 27-11 Reference to Front This value allows a maintainer to override the standard code and data End Processor Code loaded into the Front End Processor, and provide a special load for the Science Run. This reference points directly into BEP memory. If 0, then no explicit FEP load is to be used. If not 0, then the item points to the memory block which contains the load image to use. Post-launch FEP load images are uplinked into memory by the main tainer using the Write Memory function of the instrument (see Section 3.2.8.3.2 on page 108), or via a patch. This parameter is intended to be used by the maintainer of the instrument, and should be 0 during normal operations. The format of the referenced FEP Load image will be specified in the ACIS Instrument Software Detailed Design Specification (AS-BUILT), MIT 36-53200. 27-12 Event List Packing This parameter is only used when the Front End Selection Algorithm Code is in "Event Finding Mode". This value is not used when the Front End is processing raw pixels. This value selects the format to use when sending processed events. Currently, the following event-list formats are supported: Faint 1x3 and Graded 1x3. 27-13 Reference to a 1-D An observer uses this item to specify a set of 1-dimensional event Window Collection selection and processing windows to use for the Science Run. If no windows are specified, Continuous Clocking Mode shall process all events from the CCDs using processing parameters specified in this block. 27-14 Split Threshold Set These values are only used when the Front End Selection Algorithm Points is in "Event Finding Mode." These values specify the threshold above which a neighboring pixel's pulse height must be to be consid ered as part of an event. These values are used when grading events and computing the overall energy of an event. Each of these items applies to a specific CCD output node. These values can range from 0 to 4095, and each set is indexed by FEP Id. 27-15 Ignore Bad Column This value is only used when the Front End Selection Algorithm is in Map Flag "Event Finding Mode." This value controls whether or not to discard events on the basis of the CCDs list of bad columns. 27-16 Grading Selection Bit These parameters are only used when the Front End Selection Algo Map rithm is in "Event Finding Mode." This set of values selects which event grades to accept. Accepted events whose grade is indicated in this list shall be telemetered. 27-17 Event Amplitude These parameters are only used when the Front End Selection Algo Lower Bound and rithm is in "Event Finding Mode". These parameters select the mini Range mum and maximum amplitudes of accepted events. Events whose total amplitude (see Section 3.2.3.3.12) is less than the lower bound value, or greater than or equal to the lower bound plus range are not telemetered. These field's ranges are governed by the minimum and maximum corrected event amplitudes. 27-18 Re-compute Bias Flag This item indicates if the software must re-compute the pixel bias values prior to starting data processing. 27-19 Bias Algorithm Mode This parameter selects either a mean or fractile bias algorithm 27-20 Bias Rejection Criteria If the mean bias algorithm is selected, this parameter specifies the sigma rejection criteria, used to prevent pixels containing X-ray or charged particle artifacts from affecting the estimate of the bias. If the fractile algorithm is selected, this parameter specifies the index of the sorted pixel array to use to determine the bias levels. This field can range from 0 to 4095. 27-21 Compression Flag This indicates whether or not to compress raw pixel data values prior to being telemetered. 27-22 Compression Selection If raw pixel data compression is enabled, this item specifies which compression table to use. 27-23 Initial Frames to This field plus 1 specifies the number of whole exposure frames that Ignore the FEP is to ignore at the start of a bias calibration that uses this parameter block. If this value is zero, each FEP will start processing all data pixels and overclocks received after the second vsync code. Science data processing, however, always ignores the first two whole exposures. 27-24 Trickle Bias Flag This item indicates if the software must telemeter the current bias map to telemetry after it has been computed. ------------------------------------------------------------------------------------------------------------
Events produced by Continuous Clocking of the CCDs have an originating column within the CCD's Image Array. Continuous Clocking Mode has the capability to select and process events based on this column position. This selection and processing is controlled using a 1-D Window Parameter Block. Table 28 illustrates the content within a single 1-D Window, and Table 29 illustrates the content of a list of 1-D Windows.
TABLE 28. 1-Dimension Window Information (Continued)
------------------------------------------------------------------------------------------------------ Req Item Description------------------------------------------------------------------------------------------------------ 28-1 CCD Identifier This selects the CCD to which the window applies. 28-2 Window Column This specifies the position of the window in terms of the left most column within the CCD's Image Array. This position is independent of the sum ming column parameters in the Continuous Clocking Parameter Block. 28-3 Window Width This specifies the number of columns (un-summed) in the window. 28-4 Sample Cycle If processing event data, this specifies the sampling frequency of the win dow. If zero, no events are processed in the window. If one, then every event is processed, if 2, every other event is processed, if 3, every third, and so on. If processing raw pixel data, this specifies whether or not to send pixels who belong to the window. If zero, all pixels belonging to the window are discarded. If not zero, the pixels are telemetered. 28-5 Local Event When processing events, these items set the lower and upper amplitudes Amplitude Range used to select candidate events. Events whose amplitude is outside this range would be rejected. When processing raw pixel data, this parameter is ignored. ------------------------------------------------------------------------------------------------------
TABLE 29. 1-Dimension Window List Parameter Block (Continued)
----------------------------------------------------------------------------------------------------- Req Item Description----------------------------------------------------------------------------------------------------- 29-1 Parameter Block This item is a ground-supplied identifier which is echoed by the instru Identifier ment software in key portions of the science telemetry. 29-2 Window Count This item identifies the number of 1-D Windows contained in the Win dow List. This value can range from 0 to 36. This field is not actually be loaded nor telemetered, but is calculated using the length of the enclos ing command or telemetry packet. 29-3 Windows[Win This item is an array of 1-D windows. The content of these windows is dow Count] described in Table 28. The number of windows in the array is deter mined by "Window Count." -----------------------------------------------------------------------------------------------------
Due to the expected size of SRAM and PRAM loads (greater than 2Kbytes), the ACIS software shall be capable of building the SRAM and PRAM loads needed to perform a Continuous Clocking Mode, as described in Section 2.2.4 on page 23.
The following itemizes the inputs needed by the synthesizer:
The result of the build shall consist of a series of DEA SRAM and PRAM load commands to the DEA Common Subsections. The CCD Array and Selections determine which Common Subsections need to be addressed.
The row sum parameter controls the number of Frame Store rows to clock into the output registers prior to clocking out the registers. This has the effect of summing the rows as they are clocked into the output register. A sum row count of 1 indicates that no row summing is to be performed.
The column sum parameter controls the number of pixels to clock out of the output registers and integrate at the output nodes. A column sum count of 1 indicates that no column summing is to be performed.
The Output Register Clocking Mode specifies how to clock out the output registers. The number of overclock pixel sums determines how many pixels to clock out of the output registers after each row of data has been completely clocked out.
The video chain response information controls how the pixel data is processed in the DEA's analog video processing section.
The optional DEA SRAM/PRAM load override instructs the synthesizer to ignore all of the previous parameters and to load the explicitly specified SRAM and PRAM commands.
In Continuous Clocking mode, ACIS shall program the DEA's PRAM and SRAM to clock the CCDs in the following fashion:
1. Clear the Image Array, Frame Store and Serial Output Shift Registers
2. Clock a set of rows through the Image Array and Frame Store into the output registers
This is accomplished by clocking the Image Array and Frame Store by the number of rows specified by "Number of Rows to Sum" in the Continuous Clocking Parameter Block.
3. Sum a set of columns into the Output Nodes
This is accomplished by integrating a number of pixels at the output nodes as they are being clocked out of the output registers. The number of pixels to sum is determined by the "Number of Columns to Sum" contained in the Continuous Clocking Parameter Block.
4. Repeat step 3 until output registers are empty
5. Clock specified number of overclocks into the Overclock Buffer
The number of overclocks to use is specified by the "Number of Overclock Pairs" in the Continuous Clocking Parameter Block.
6. Repeat from 2.
The time it takes to clock out one row from the Output Registers (steps 3-5) shall be no greater than 6.5ms. The goal is to clock out the rows as fast as the hardware allows.
The overclocking processing for Continuous Clocking Science Mode is almost identical to that for Timed Exposure Science Mode, except the number of clocks and exposures are specified via the Continuous Clocking Parameter Block. Refer to Section 3.2.2.3.6 on page 62 for a description of these requirements.
The pixel-by-pixel bias map values are computed when configured by the parameter block, instructed by a "Compute Bias" command, or when the bias maps are invalid. Prior to processing events, the Front End Processor shall use one or more exposures to compute a output node-specific "Initial Overclock" values, and a pixel-by-pixel bias level and store the result in the Front End's Pixel Bias Map.
(EQ 8) Pixel Bias Map Value = Computed Pixel Bias + Initial Overclock
The algorithm to use to compute the bias is determined by the "Bias Algorithm Mode" parameter of the Continuous Clocking Parameter Block. The chosen algorithm may be tuned using the "Bias Rejection Criterea" of the same block.
The Front End Processor software shall compute the CCD threshold according to the following formula:
(EQ 9) Threshold Register Value = Threshold Set Point + Overclock Level - Initial Overclock
The Front End Processor software shall set the threshold registers with the computed values prior to each set of 512 rows.
The Front End Processor contains a Pixel Threshold BitMap. This bitmap indicates which pixels in the acquired CCD data have pulse heights greater their respective output -node threshold registers plus their respective pixel bias map values. The bit corresponding to a pixel is set if:
(EQ 10) Pixel Pulse Height > Pixel Bias Map Value + Threshold Register Value
When the "Front End Selection Algorithm" field of the Continuous Clocking Parameter Block indicates the Event-finding mode, the Front End Processor software shall scan this bitmap for each exposure. Any pixel marked as above its threshold shall be counted in an "above threshold" counter, and be tested as an event. Refer to Section 3.2.3.3.9 on page 87 for the Event-finding requirements.
The threshold map is ignored for all Front End Modes except "Event-finding Mode."
When the "Front End Selection Algorithm" field of the Continuous Clocking Parameter Block indicates the Event-finding mode, the Front End Processor selects events from candidates indicated by the hardware Pixel Threshold Map. If a pixel is indicated in this map, the Front End software compares the corrected pulse height of the pixel (see Section 3.2.3.3.12 on page 88) to each pixel on either side of the candidate. If the candidate's pulse height is greater than or equal to the pixel immediately preceding it in the row, and greater than the pixel immediately following it in the row, the Front End processor forwards the 3 pixels to the Back End processor for further selection and processing.
Each Front End shall be capable of testing at least 1000 candidate events per second, and the total number of events capable of being produced by all of the Front Ends shall be at least 750 events per second (assuming unbounded telemetry).
When the "Front End Selection Algorithm" field of the Continuous Clocking Parameter Block indicates "Raw Mode", the Front End processor merely passes raw pixel data to the Back End Processor as it is poured into the Front End's image buffer.
The Back End Processor shall contain a list of bad columns from each CCD. This Bad Column Map is edited using maintenance commands from the ground (see Section 3.2.7 on page 99). The Bad Column Map entries provide the information described in Table 30.
TABLE 30. Bad Column Map Content (Continued)
--------------------------------------------------------------------------------------------- Req Item Description--------------------------------------------------------------------------------------------- 30-1 CCD Id The Bad Column Map must contain enough information to identify the CCD to which the bad column applies. 30-2 Column Id The Bad Column Map must contain enough information to identify which col umn in the CCD is bad. ---------------------------------------------------------------------------------------------
When the "Front End Selection Algorithm" field of the Continuous Clocking Parameter Block indicates the Event-finding mode, and the "Ignore Bad Column Map Flag" is de-asserted, the software shall test any events generated by the Front End to ensure that the center pixel of the 1x3 event is not listed in the Bad Column Map. If the center pixel is in the list, no further processing on the event takes place. If the center of the event is not in the list, the software accepts the event for further selection and processing.
Pixels belonging to a bad column which surround the center pixel of an event shall be treated as having a pulse-height of 0.
The Bad Column maps are ignored for all Front End Modes except "Event-finding Mode."
To obtain the corrected pulse height of a pixel, the ACIS Science Instrument Software subtracts the corresponding output node overclock level, computed bias value (i.e. the bias map value minus the global initial overclock) from each pixel in the 1x3 group, to obtain a bias corrected pulse height of each pixel.
(EQ 11) Corrected Pixel PH = raw pixel ph - pixel bias value - (overclock - initial overclock)
The ACIS software shall compute the corrected event amplitude of a 1x3 group of pixels by summing the corrected pulse heights of all 3 pixels which are greater than the "Split Threshold," as specified in the Continuous Clocking Parameter Block (see Table 3.2.3.3.1).
When the "Front End Selection Algorithm" field of the Continuous Clocking Parameter block indicates an Event-finding mode, the Back End Processor shall compute the overall corrected amplitude of the 1x3 events received from the Front End, and compare the result with the "Event Amplitude Lower Bound and Range", specified in the parameter block.
If the value is less than the lower bound, or greater than or equal to the lower bound plus the range, the software shall increment the "amplitude" event rejection counter, and discard the event. If the value is within range, the software shall accept the event for further selection and processing.
Event Amplitude selection only applies when the "Front End Selection Algorithm" field indicates "Event-finding Mode."
When required to do so, the Back End software shall compute the "grade" of a 1x3 pixel event. To accomplish this, the software compares the corrected pulse heights of the 2 outside pixels of the event to the "Split Threshold" specified in the Continuous Clocking Parameter Block. This threshold is dependent on the number of summed rows and columns and therefore does not need to be scaled.
Each outside pixel corresponds to a bit in the 2-bit grade code. If a pixel's pulse height is above the "Split Threshold", the corresponding bit is set to `1'. If below the threshold, the pixel's bit is set to 0.
When the "Front End Selection Algorithm" field of the Continuous Clocking Parameter Block indicates an Event-finding mode, and the "Grading Selection Bitmap" does not indicate that all possible grades are to be accepted, the Back End software shall compute the grade of an event and compare the computed grade to the list of desired grades. If the computed grade is not in the list, the event is counted and discarded. If the event's grade is in the list, the event is accepted for further selection and processing.
Grade-based event selection only applies when the "Front End Selection Algorithm" field indicates "Event-finding Mode," and when the "Grading Selection Bitmap" indicates that only a subset of grades are to be processed (i.e. if all grades are accepted, no grade-based selection operation is performed).
The Back End software shall use 1-D windows to select events and pixels to telemeter. If an event's center pixel, or an individual pixel's position is within the bounds of a 1-D window, it is processed according to the window's selection code. For a given event or pixel, each window in the window list is checked in the order they are presented in the list. If the event/pixel column is within the bounds of the window, the event/pixel is processed by the window. The window boundaries are expressed independently of the number of summed columns. Therefore, the pixel position, relative to a window, is really a range of positions. If this range intersects the window, it is considered a match, and event is selected by the window. If the position is outside the bounds of the window, the next window is checked. This continues until either a match is found, or until the list is exhausted.
If no window list is specified, or if the list becomes exhausted with the event/pixel not being picked up by any of the windows, the event/pixel is, by default, accepted for processing.
The precise processing modes for the windows are the same as those described for Timed Exposure Mode (see Section 3.2.2.3.18 on page 67).
The Back End software produces raw event telemetry when the "Front End Selection Algorithm" field of the Timed Exposure Parameter Block indicates a "Raw" mode. In this mode, contiguous regions of 512 rows of pixels are telemetered as a set. For each 512 rows, a "Continuous Raw Mode Record" is formed and telemetered. Table 31 lists the elements telemetered for each pixel and Table 32 identifies the components of a Continuous Raw Mode Record.
TABLE 31. Continuous Raw Mode Data Telemetry (Continued)
---------------------------------------------------------------------------------------------------------- Req Item Description---------------------------------------------------------------------------------------------------------- 31-1 Packet Synch This field marks the start of the ACIS packet within the telemetry stream. 31-2 Packet Word This field indicates the number of 32-bit words in the packet. Length 31-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Continuous Clocking Raw Mode data packet. 31-4 Packet Sequence This field is used to sequentially number all ACIS telemetry packets. Number 31-5 CCD/FEP Identi These identify which CCD and FEP produced the raw pixel data. fiers 31-6 Data Packet Num Since data from different CCDs can be interleaved, and also mixed with ber other kinds of packets, this field sequentially numbers the data packet for a given CCD exposure. 31-7 Compression These fields indicate whether or not the raw data has been compressed, Selection Flag and and if so, by which compression table. Table Selection 31-8 Pixel Position This specifies the row and column of the first pixel in the packet, relative to the start of a 512 row block. 31-9 Packed or com This consists of an array of window-selected raw CCD pixel data. Pixels pressed collection filtered out by the window processing are dropped. This forces the of raw 12-bit CCD ground to use knowledge of the chosen 1-D windows to reconstruct the pixel and over image. The packed pixels are output row by row, starting from the first clock data row clocked out of the CCD, with the overclock data for a given row sent immediately after the pixel data for the row. Overclock pixels are always sent, even if the row is completely filtered out by the 1-D windows. Unused bits at the end of the telemetry packet (needed to fill out to the nearest 32-bit word boundary) will be zero. ----------------------------------------------------------------------------------------------------------
TABLE 32. Continuous Raw Mode Record Content (Continued)
--------------------------------------------------------------------------------------------------------- Req Item Description--------------------------------------------------------------------------------------------------------- 32-1 Packet Synch This field marks the start of the ACIS packet within the telemetry stream. 32-2 Packet Word This field indicates the number of 32-bit words in the packet. Length 32-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Continuous Clocking Raw Mode Exposure Record packet. 32-4 Packet Sequence This field is used to sequentially number all ACIS telemetry packets. Number 32-5 Science Run Start This identifies the start time of the science run, relative to when the Time DEA interface latched the ACIS time-stamp at the start of the run. 32-6 Continuous Clock This item is a copy of the Continuous Clocking Parameter Block Identi ing Parameter fier used to configure the current run. Block Identifier 32-7 Window Block This item is a copy of the Window List Parameter Block Identifier used Identifier to configure the current run. If no Window List was specified, this field will be 0xffffffff. 32-8 FEP Timestamp This is the value of the FEP time-stamp counter when the exposure arrived from the CCD. 32-9 Exposure Number This uniquely identifies the group of events during the run. This field must allow the ground to uniquely identify over 259,200 sets of 512 rows (exposures) during a single run (1 second/exposure for 72 hours). 32-10 CCD/FEP Identi This identifies from which CCD and FEP the raw pixel data was taken. fier 32-11 Pixel Count This specifies the total # of pixels being sent for the exposure from the CCD. ---------------------------------------------------------------------------------------------------------
The Back End software produces Faint Mode event telemetry when the "Event Packing Code" field of the Continuous Clocking Parameter Block indicates "Faint" packing mode. This mode applies only when the Front End Processor is in "Event-finding mode." In this mode, a series of distinct events are telemetered as 1x3 arrays of pixels. Table 33 illustrates the content of the Faint-Mode event lists, and Table 34 illustrates the content of a Continuous Faint Mode Record.
TABLE 33. Continuous Faint Mode Event Data (Continued)
------------------------------------------------------------------------------------------------ Req Item Description------------------------------------------------------------------------------------------------ 33-1 Packet Synch This field marks the start of the ACIS packet within the telemetry stream. 33-2 Packet Word Length This field indicates the number of 32-bit words in the packet. 33-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Continuous Clocking Faint-Mode Event data packet. 33-4 Packet Sequence Num This field is used to sequentially number all ACIS telemetry pack ber ets. 33-5 CCD/FEP Identifiers These identify which CCD and FEP produced the event 33-6 Data Packet Number Since data from different CCDs can be interleaved, and also mixed with other kinds of packets, this field sequentially numbers the data packet for a given CCD exposure. The remainder of the packet contains zero or more of the following: 33-7 Row Identifier This identifies from which (possibly summed) row the event was acquired, relative to the 512 row block. This value can be used to obtain a high-resolution time-stamp of the event, knowing the row rate from the CCD. 33-8 Column Identifier This identifies from which (possibly summed) column the event was acquired. 33-9 Uncorrected Pulse These items are the measured (uncorrected) pulse heights of the 3 Heights pixels of the event's 1x3 array. ------------------------------------------------------------------------------------------------
TABLE 34. Continuous Faint Mode Record Content (Continued)
------------------------------------------------------------------------------------------------------ Req Item Description------------------------------------------------------------------------------------------------------ 34-1 Packet Synch This field marks the start of the ACIS packet within the teleme try stream. 34-2 Packet Word Length This field indicates the number of 32-bit words in the packet. 34-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Continuous Clocking Faint Mode Record 34-4 Packet Sequence Num This field is used to sequentially number all ACIS telemetry ber packets. 34-5 Science Run Start Time This identifies the start time of the science run, relative to when the DEA interface latched the ACIS time-stamp at the start of the run. 34-6 Continuous Clocking This item is a copy of the Continuous Clocking Parameter Block Parameter Block Identi Identifier used to configure the current run. fier 34-7 Window Block Identifier This item is a copy of the Window List Parameter Block Identi fier used to configure the current run. If no Window List was specified, this field will be 0xffffffff. 34-8 Bias Start Time This identifies the start time of the most recently computed bias map, relative to when the DEA interface latched the ACIS time- stamp at the start of the bias computation. 34-9 Bias Parameter Block This item is a copy of the Parameter Block Identifier used to Identifier configure the most recent bias map computation. 34-10 CCD/FEP Identifiers These identify which CCD and FEP produced the exposure 34-11 FEP Timestamp This is the value of the FEP time-stamp counter when the expo sure arrived from the CCD. 34-12 Continuous Faint Mode This uniquely identifies a stream of data within the run. This Exposure Number field must allow the ground to uniquely identify over 130,000 records during a single run (2 second exposures for 72 hours). 34-13 Number of Events This specifies the number of events being telemetered as part of this event stream. This field must accommodate at least 64K events. 34-14 Number of Pixels above This specifies the total number of (possibly summed) pixels Threshold whose pulse heights were above the threshold. 34-15 Number of Events Dis These specifies the number of events which were discarded due carded by Amplitude to their amplitude. This field must accommodate the total num ber of pixels within the CCDs. 34-16 Number of Events Dis These specify the number of events which were discarded due to carded by Grade their "grade." 34-17 Number of Events Dis These specify the number of events which were discarded by the carded by Window processing windows. 34-18 Overclock Levels These identify the overclock levels used for the thresholding during the exposure which produced the events. 34-19 Bias Map Parity Hit This specifies the total number of pixels disabled due to parity Count hits in the corresponding bias map location. ------------------------------------------------------------------------------------------------------
The Back End software produces Graded event telemetry when the "Event Packing" Code" field of the Continuous Clocking Parameter Block indicates a "Graded" packing mode. This mode applies only when the Front End Processor is in "Event Finding Mode," as indicated by the "Front End Selection Algorithm." In this mode, sets of distinct events are telemetered using reduced event amplitude information and event "Grade" (see Section 3.2.3.3.14 on page 89). The content of a Continuous Graded Event Record in this mode is identical to that used by Continuous Faint Mode Telemetry (see Section 3.2.3.3.18 on page 91). The event data content, however, is different. Table 35 illustrates the content of the event lists telemetered when in this mode.
TABLE 35. Continuous Graded Mode Event Data Telemetry (Continued)
------------------------------------------------------------------------------------------------------- Req Item Description------------------------------------------------------------------------------------------------------- 35-1 Packet Synch This field marks the start of the ACIS packet within the telemetry stream. 35-2 Packet Word Length This field indicates the number of 32-bit words in the packet. 35-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Continuous Clocking Graded Mode data packet. 35-4 Packet Sequence This field is used to sequentially number all ACIS telemetry packets. Number 35-5 CCD/FEP Identifiers These identify which CCD and FEP produced the event 35-6 Data Packet Number Since data from different CCDs can be interleaved, and also mixed with other kinds of packets, this field sequentially numbers the data packet for a given CCD exposure. The remainder of the packet contains zero or more of the following: 35-7 Row Identifier This identifies from which (possibly summed) row the event was acquired. This value is used to obtain a high-resolution time-stamp of the event. 35-8 Column Identifier This identifies from which (possibly summed) column the event was acquired. 35-9 Event Amplitude This item is the corrected amplitude of the 1x3 event. 35-10 Grade Code This identifies the Grade Code of the event. See Section 3.2.3.3.14 on page 89 for a description of how this is computed. -------------------------------------------------------------------------------------------------------
When configured to re-compute and telemeter the bias maps, the instrument software shall trickle the pixel bias maps from each of the active Front End Processors, into the telemetry stream. The algorithm used shall ensure a 10% minimum utilization of the telemetry stream. The algorithm may consume under-utilized telemetry.
TABLE 36. Continuous Pixel Bias Map Telemetry Content (Continued)
-------------------------------------------------------------------------------------------------------- Req Item Description-------------------------------------------------------------------------------------------------------- 36-1 Packet Synch This field marks the start of the ACIS packet within the telemetry stream. 36-2 Packet Word This field indicates the number of 32-bit words in the packet. Length 36-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Continuous Clocking Bias Map packet. 36-4 Packet Sequence This field is used to sequentially number all ACIS telemetry packets. Number 36-5 Bias Start Time This identifies the start time of the bias run, as specified by the DEA latched ACIS time-stamp. 36-6 Continuous This item is a copy of the Continuous Clocking Parameter Block Identi Clocking Param fier used to configure the current run. eter Block Identi fier 36-7 CCD/FEP Identi These identify which CCD and FEP produced the bias map fiers 36-8 Initial Overclock This specifies the initial overclock value added to every pixel bias map value. 36-9 Pixels Per Row This specifies the number of pixel bias values per row 36-10 Bias Map Data This is a bit-packed array of the single row of bias map data. NOTE: Unlike Timed Exposure Mode, this data is not compressed. --------------------------------------------------------------------------------------------------------
The diagnostic extensions of this mode are described in more detail by Section 3.2.5 on page 97. The extensions specific to Continuous Clocking Mode include:
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