Built-in Variables

Built-ins are variables and parameters that are dedicated to well defined aspects of the TRACE observations. These include things like the location of the IMAX, the indicator that a flare event has happened, or the number of flare buffers available. Some built-ins are values returned from the DHC. Built-in variables are listed in Table 1 and defined in the paragraphs that follow. The built-ins occupy sequencer registers 27-47. The first 3 built-ins have no special meaning to the sequencer per se. These are used by convention to signify specific orbital events. A sequence may use these flag as it would any other variables to control flow.

Name	Register	Description
$SAA	27	South Atlantic Anomaly
$HLF	28	High Latitude Flag
$AAZ	29	Atmospheric Absorption Zone
	30	Spare
$MMS	31	Mass Memory Status
$FEF	32	Flare Event Flag
$SEF	33	Super Event Flag
$TEF	34	Transient Event Flag
$NBF	35	Number of Buffers
$CBF	36	Current Buffer
$TRC	37	Target Class
$MXR	38	IMAX Row Number
$MXC	39	IMAX Column number
$MXV	40	IMAX Value
$MNR	41	IMIN Row Number
$MNC	42	IMIN Column number
$MNV	43	IMIN Value
$RTN	44	Sequence Exit Status
$PRI	45	Sequence Priority
$PND	46	Sequence Pending
	47	Spare

Table 1 Built-in Variables

South Atlantic Anomaly ($SAA)

By convention, this flag is set from the timeline at or before the spacecraft enters the SAA and cleared from the timeline upon exit from the SAA. The sequencer takes no specific action based on this flag, but rather, each sequence responds in whatever way is deemed appropriate for that sequence.

High Latitude Flag ($HLF)

By convention, this flag is set from the timeline at or before the spacecraft enters the High Latitude Zone and cleared from the timeline upon exit from that zone. The sequencer takes no specific action based on this flag, but rather, each sequence responds in whatever way is deemed appropriate for that sequence.

Atmospheric Absorption Zone ($AAZ)

By convention, this flag is set from the timeline at or before the spacecraft enters the Atmospheric Absorption Zone and cleared from the timeline upon exit from that zone. The sequencer takes no specific action based on this flag, but rather, each sequence responds in whatever way is deemed appropriate for that sequence

Spare Mass Memory Status ($MMS)

The format of $MMS is shown in Table 2. For each file, S[hort]1 - S[hort]4 and M[ain]F[ile], the DLE bits indicate the following:

D: Set if the file is currently being downlinked.

L: Set if the file is currently locked.

E: Set if the file is currently empty.

The last status bit S is set if any downlink is in progress and is a general indicator that the spacecraft is in a station contact. The information in $MMS is gleaned from the mass memory status command which the TRACE instrument receives from the SCS each 5 seconds.

Bits(r)	15	14	13	12	1 1	10	9	8	7	6	5	4	3	2	1	0
		MFStatus			S4Status			S3Status			S2Status			S1Status
	S	D	L	E	D	L	E	D	L	E	D	L	E	D	L	E

Table 2 Mass Memory Status Word

Flare Event Flag ($FEF)

$FEF is set if the flare criteria was satisfied by the most recent frame that requested a flare check. The flag is reset automatically the next time a flare check is requested and not satisfied.

Super Flare Event Flag ($SEF)

$SEF is set if the flare criteria was satisfied by the most recent frame that requested a super flare check. The flag is reset automatically the next time a super flare check is requested and not satisfied.

Transient Event Flag ($TEF)

$TEF is set if the transient criteria was satisfied by the most recent frame that requested a transient check. The flag is reset automatically the next time a transient check is requested and not satisfied.

Number of Buffers ($NBF)

$NBF contains the number of flare buffers that are currently unlocked. There are four flare buffers. The LOCKBUF instruction locks the current buffer then sets the current buffer to the next unlocked buffer. The CC unlocks each buffer when the memory status command from the spacecraft indicates that the buffer is empty and thus has been dumped.

Target Class ($TRC)

$TRC contains the two bit target class field from the current target.

Row Number Of IMAX ($MXR)

$MXR contains the row number of the most recent IMAX. If an event has occurred, it contains the row number of that of the event. $MXR is always set to the row number as read from amplifier A.

Column Number Of IMAX ($MXC)

$MXC contains the column number of the most recent IMAX. If an event has occurred, it contains the column number of that of the event. $MXC is always set to the column number as read from amplifier A.

Maximum Value ($MXV)

$MXV contains the number of counts in the most recent event or IMAX. The value has been adjusted so it represents counts per pixel. If the counts exceed that which can be expressed as a 16 bit number, $MXV is set to all 1's

Row Number Of IMIN ($MNR)

$MNR contains the row number of the most recent IMIN. $MNR is always set to the row number as read from amplifier A.

Column Number Of IMIN ($MNC)

$MNR contains the column number of the most recent IMIN. $MNC is always set to the column number as read from amplifier A.

Minimum Value ($MNV)

$MNV contains the number of counts in the most recent event or IMIN. The value has been adjusted so it represents counts per pixel.

Return Status ($RTN)

$RTN contains the value specified on the most recent EXIT instruction.

Priority ($PRI)

$PRI contains the priority flag. If the values is zero, the priority is low; otherwise, it is high. When a sequence is started by the new sequence command, $PRI contains the value of the priority parameter on that command.

Sequence Pending ($PND)

$PND indicates that a sequence is pending. This occurs if the current sequence is high priority and the new sequence command is low priority.

Repeat Count ($RPT)

$RPT contains the current value of the count used by the repeat instruction. $RPT counts up from 0.