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This section specifies additional instrument software features which have been requested, but are not part of the core system requirements. These features may or may not delivered as part of the final instrument software release, depending on the availability of development and testing resources.
NOTE: In order to improve the spectral resolution of Back-Side illuminated CCDs, Faint 5x5 Mode has been added to the ACIS Flight Software. However, due to the extremely low event rate supported by Faint-with-Bias 5x5 Mode, the Faint-with-Bias variation has not been added.
This is a variant of Timed Exposure Faint Mode and Faint-with-Bias Mode. All event selection is performed in the same fashion as when the "Front End Selection Algorithm" is in "Event-finding Mode," except that the Front End's include the additional 16 pixels surrounding a detected 3x3 event when transferring the event to the Back End Processor. The Back End grades and filters the events as if they were 3x3 events, but includes the additional 16 pixels in the telemetry stream.
Addition of this feature modifies the existing requirements in the following ways:
1. Table 11: Add one new value to "Front End Selection Algorithm", "Event-finding 5x5" to cause the Front End to send the additional pixels with each event.
2. Table 11: Add two new values to "Event List Packing Code", "Faint 5x5" and "Faint-with-Bias 5x5". "Faint 5x5" produces Faint Mode telemetry with the additional 25 pixels packed into the telemetry data packets. "Faint-with-Bias 5x5" adds the corresponding 25 pixel bias values to the data packets.
3. Section 3.2.2.3.10: Indicate that when the FEP is in "Event-finding 5x5" mode, it is required to transfer the 16 surrounding pixel and bias values to the Back End processor with each detected event.
In addition to these changes, the following two subsections are added to Section 3.2.2.
The Back End software produces Faint Mode 5x5 event telemetry when the "Event List Packing Code" field of the Timed Exposure Parameter Block indicates a "Faint 5x5" packing mode. This mode applies only when the Front End Processor is in "Event-finding 5x5" mode as indicated by the "Front End Selection Algorithm." In this mode, sets of distinct events are telemetered as 5x5 arrays of pixels. Table 80 illustrates the content of the Faint-Mode 5x5 event list data packet. This mode uses the same Exposure Record format used by Faint-Mode (see Section 3.2.2.3.21).
TABLE 80. Faint 5x5 Mode Exposure Event Data (Continued)
------------------------------------------------------------------------------------------------------------- Req Field Description------------------------------------------------------------------------------------------------------------- 80-1 Packet Synch This field marks the start of the ACIS packet within the telemetry stream. 80-2 Packet Word Length This field indicates the number of 32-bit words in the packet. 80-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Timed Exposure Faint-Mode data packet. 80-4 Packet Sequence Number This field is used to sequentially number all ACIS telemetry packets. 80-5 CCD/FEP Identifiers These identify which CCD and FEP produced the event 80-6 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: 80-7 Position Identifier This identifies the row and column of the center pixel of the event 80-8 Uncorrected Pulse Heights. If not zero, these items are the measured (uncorrected) pulse heights of the 25 pixels of the event's 5x5 array. -------------------------------------------------------------------------------------------------------------
The Back End software produces Faint Bias 5x5 Mode event telemetry when the "Event List Packing Code" field of the Timed Exposure Parameter Block indicates a "Faint-Bias 5x5" packing mode. This mode applies only when the Front End Processor is in "Event-finding 5x5" mode as indicated by the "Front End Selection Algorithm." In this mode, sets of distinct events are telemetered as 5x5 arrays of pixels along with the corresponding pixel bias values. Table 81 illustrates the content of the Faint-Bias Mode event list data packet. The exposure record format used by this mode is identical to that used by Faint-with-Bias Mode (see Section 3.2.2.3.22).
TABLE 81. Faint-Bias 5x5 Mode Exposure Data Content (Continued)
------------------------------------------------------------------------------------------------- Req Field Description------------------------------------------------------------------------------------------------- 81-1 Packet Synch This field marks the start of the ACIS packet within the telemetry stream. 81-2 Packet Word Length This field indicates the number of 32-bit words in the packet. 81-3 Format Tag This field indicates the type of data contained in the teleme try packet, in this case a Timed Exposure Faint-Bias Mode data packet. 81-4 Packet Sequence Number This field is used to sequentially number all ACIS telemetry packets. 81-5 CCD/FEP Identifiers These identify which CCD and FEP produced the event 81-6 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: 81-7 Position Identifier This identifies the row and column of the center pixel of the event 81-8 Uncorrected Pulse Heights These items are the measured (uncorrected) pulse heights of the 25 pixels of the event's 5x5 array. 81-9 Pixel Bias Map Values These are the computed pixel bias values associated with the event's 25 pixels. -------------------------------------------------------------------------------------------------
This is a distinct processing mode. It uses the standard Front End "Event-finding" mode to produce events with each exposure, and filters the events on the Back End Processor. Rather than telemetering the events, however, the Back End Processor builds histograms of the event amplitudes. There is one histogram for each CCD output node, and each histogram contains at least 4097 amplitude bins. A bin is advanced by 1 whenever an event whose amplitude matches the bin number is accepted. Each bin must be capable of counting at least 64K events. Bins 0 through 4095 correspond to events whose amplitudes correspond to the respective bin number. Bin 4096 corresponds to all accepted events whose amplitude is greater than 4095.
Addition of this feature modifies the existing requirements in the following ways:
1. Table 11: Add a new value to "Event List Packing Code", "Event Amplitude Histogram, which causes the Back End Processor to produce histograms of event amplitudes, rather than telemetering the events themselves.
2. Table 11: Modify the name and description of the "Raw Histogram Exposure Count" to allow it to specify the number of exposures to be accumulated into the event amplitude histograms.
In addition to these changes, the following subsection is added to Section 3.2.2.
The Back End software produces "Event Amplitude Histogram Mode" telemetry when the Front End Processor is in "Event-finding Mode," as indicated by the "Front End Selection Algorithm" and the "Event List Packing Code" indicates "Event Amplitude Histogram" mode.
When in this mode, the Back End Processor will filter events received from the Front End Processor. The amplitude of each accepted event is then accumulated into a CCD output-node specific histogram. Once the desired number of exposures has been processed, the Back End will telemeter the generated histograms, and then proceed to process the next collection of exposures. Table 82 illustrates the data packet telemetry content for this mode and Table 83 illustrates the content of an Exposure Record used with Event Amplitude Histogram mode.
TABLE 82. Event Amplitude Histogram Data (Continued)
---------------------------------------------------------------------------------------------------- Req Field Description---------------------------------------------------------------------------------------------------- 82-1 Packet Synch This field marks the start of the ACIS packet within the teleme try stream. 82-2 Packet Word Length This field indicates the number of 32-bit words in the packet. 82-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Timed Exposure Histogram data packet. 82-4 Packet Sequence Number This field contains the packet sequence number. 82-5 CCD/FEP Identifiers These identify which CCD and FEP produced the histogram. 82-6 Data Packet Number Since data from different CCDs can be interleaved, and also mixed with other kinds of packets, this field sequentially num bers the data packet for a given set of CCD histograms. 82-7 Output Node Identifier This identifies from which output node the histogram was formed. 82-8 Starting Bin Number This item is the index of the first histogram bin contained within the packet. 82-9 Array of histogram counts This consists of an array of adjacent histogram bins. Each bin contains a count of the number of accepted events from the specified output node whose amplitude corresponded to the bin index. ----------------------------------------------------------------------------------------------------
TABLE 83. Event Amplitude Histogram Record Content (Continued)
------------------------------------------------------------------------------------------------------ Req Field Description------------------------------------------------------------------------------------------------------ 83-1 Packet Synch This field marks the start of the ACIS packet within the teleme try stream. 83-2 Packet Word Length This field indicates the number of 32-bit words in the packet. 83-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Timed Exposure Event Amplitude Histo gram Record packet. 83-4 Packet Sequence Number This field contains the packet sequence number. 83-5 Science Run Start Time This identifies the start time of the science run using the ACIS time-stamp latched by the hardware at the start of the run. 83-6 Timed Exposure Parameter This item is a copy of the Timed Exposure Parameter Block Block Identifier Identifier used to configure the current run. 83-7 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 zero. 83-8 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. 83-9 Bias Parameter Block Iden This item is a copy of the Parameter Block Identifier used to tifier configure the most recent bias map computation. 83-10 CCD/FEP Identifiers These identify which CCD and FEP produced the histogram. 83-11 Output Node Identifier This identifies from which output node the histogram was formed. 83-12 First Exposure Number This uniquely identifies the first exposure acquired into the his togram during the run. 83-13 Last Exposure Number This uniquely identifies the last exposure acquired into the his togram during the run. 83-14 Number of Exposures Pro This identifies the total number of exposures acquired in the cessed histogram. Since one or more exposures may be dropped or ignored, this may be different than the "Exposure Number" listed above. 83-15 Number of Pixels above These specify the total number of pixels from a CCD whose threshold pulse heights were above their respective spatial thresholds during the exposure. 83-16 Number of Events Dis These specify 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. 83-17 Number of Events Dis These specify the number of events which were discarded due carded by Grade to their "grade." 83-18 Number of Events Dis These specify the number of events which were discarded by carded by Window the processing windows. 83-19 Bias Map Parity Hit Count This specifies the total number of pixels disabled due to parity hits. ------------------------------------------------------------------------------------------------------
This feature allows the maintainer to monitor specific pixels in the CCD on every exposure when the Front End Processor is in "Event-finding Mode", regardless of whether an event is detected in the pixel or not. The list of fiducial pixels are maintained in the Bad Pixel Map (see Section 3.2.2.3.13, Section 3.2.7.3.4 and Section 3.2.7.3.5). Entries are added using the "Add Bad Pixel" command, and are discarded whenever the bad pixel map is reset. The system will support a maximum of 128 fiducial entries per CCD. The set of fiducial pixels is produced by the Front End Processor for each exposure and forwarded to the Back End Processor. The Back End then compresses and telemeters the set.
Addition of this feature modifies the existing requirements in the following ways:
1. Table 11: Add a field to the table, indicating if a FEP should produce fiducial pixels for this run or not.
2. Table 14: Add a field indicating whether the entry is a Bad Pixel or a Fiducial Pixel.
3. Section 3.2.2.3.10: Add description indicating that the Front End must locate and forward fiducial pixels to the Back End Processor on each exposure.
4. Section 3.2.7.3.4: Add field to indicate whether an entry is a bad pixel or a fiducial pixel.
In addition to these changes, the following subsection is added to Section 3.2.2.
Whenever the Front End Processor is in "Event-finding Mode", it forwards zero or more pairs of fiducial pixel entries to the Back End Processor. On each exposure, the Back End Processor then compresses the set of fiducial pixel data and telemeters the set, using the raw data compression table selection. NOTE: If a fiducial is dropped (for whatever reason), it is represented using the value 4095 prior to compression. Table 84 illustrates the content of a fiducial pixel data telemetry packet.
TABLE 84. Fiducial Pixel Data Telemetry Content (Continued)
------------------------------------------------------------------------------------------------------- Req Field Description------------------------------------------------------------------------------------------------------- 84-1 Packet Synch This field marks the start of the ACIS packet within the telem etry stream. 84-2 Packet Word Length This field indicates the number of 32-bit words in the packet. 84-3 Format Tag This field indicates the type of data contained in the telemetry packet, in this case a Timed Exposure Parity Error data packet. 84-4 Packet Sequence Number This field is used to sequentially number all ACIS telemetry packets. 84-5 Science Run Start Time This identifies the start time of the science run using the ACIS time-stamp latched by the hardware at the start of the run. 84-6 Timed Exposure Parameter This item is a copy of the Timed Exposure Parameter Block Block Identifier Identifier used to configure the current run. 84-7 CCD/FEP Identifiers These identify which CCD and FEP produced the event 84-8 Exposure Number Since data from different CCDs can be interleaved, and also mixed with other kinds of packets, this field sequentially num bers the fiducial packet for a given CCD exposure. 84-9 Fiducial Count This specifies the total # of fiducial pixels sent for the expo sure from the CCD. 84-10 Compression Selection Flag These fields indicate whether or not the raw data has been and Table Selection compressed, and if so, by which compression table. 84-11 Packed or compressed col This consists of an array of possibly compressed fiducial pixel lection of raw 12-bit CCD data. fiducial pixel pairs -------------------------------------------------------------------------------------------------------