4.5 Data System

 

4.5.16 Commands

 

Command Processing. The data system processes 16-bit serial data commands received from ground control via the S/C. The commands are used to control the operating modes of the experiment. All commands are executed at the end of a data input cycle, and up to 15 commands may be stored before execution. There are 21 command types, of which at most 17 would be useful at one time. Of the 216 possible bit patterns, 2591, or 4%, are valid commands.

 

Limitations. It should be noted that the S/C uplink or hardware may limit the rate at which the data system can receive commands. Also, when two or more commands are generated, it is possible that they will not be received during the same data cycle. The command pending bit of the status preamble indicates whether a received command has been executed.

 

Structure. The structure of each command type is shown in Table 4.16. The data system receives the MSB first. The parity bit P is chosen such that the total number of "ones" including the parity bit is odd. All bits must be as specified; there are no "don't care" bits.

 

Table 4.16 Command structure

 

COMMAND TYPE	ADDRESS MSB	DATA		PARITY LSB
*LAG	011	011NT8	T7T6T5T4T3T2T1	P
SECTOR, TIME	011	00000	U7U6U5U4U3U2U1	P
SECTOR, AUTO	011	00001	U7U6U5U4U3U2U1	P
IC, AUTO	011	00101	A7A6A5A4A3A2A1	P
IC, FIXED	011	00110	A7A6A5A4A3A2A1	P
CA PHA, AUTO	011	00111	00000P2P1	P
CA PHA, FIXED	011	00111	00000P2P1	P
CA PHA, RESET	011	00111	0001000	P
SINGLES, AUTO	011	01001	0000000	P
SINGLES, FIXED	011	01001	00100S2S1	P
MFSA POINTER	011	10000	0000M3M2M1	P
POWERDOWN RESET	011	10100	0000010	P
*COVER A	011	10100	000010C	P
*COVER B	011	10100	000011D	P
OUTPUT-1 SET	011	0001W8	W7W6W5W4W3W2W1	P
OUTPUT-1 RESET	010	0001W8	W7W6W5W4W3W2W1	P
OUTPUT-2 SET	011	0101X8	X7X6X5X4X3X2X1	P
OUTPUT-2 RESET	010	0101X8	X7X6X5X4X3X2X1	P
OUTPUT-3 SET	011	1001Y8	Z7Z6Z5Z4Z3Z2Z1	P
OUTPUT-2 RESET	010	1001Y8	Z7Z6Z5Z4Z3Z2Z1	P
IC POWER	011	10110	EOOOOOO	P

 

*no validation indicators in data stream

 

Function. The function of each command type and the command meaning of the bits composing the commands are described in this section.

 

1. Lag Command. The lag command determines the lag between the occurrence of the sun pulse and the beginning of a spin, when the data system is in the sun sectoring mode. The N bit specifies the number of complete sectors that must pass before the spin starts; a 0 corresponds to 0 sectors, a 1 corresponds to 1 complete sector. The T bits specify the additional fraction of a sector that must pass before the spin starts. T8...T1 can range from 00 to DB (hex). If a value greater than 'DB' is specified, 'DB' will be used. The value of T8 is 1/2 sector duration; that of T1 is 1/256 sector duration. Note that sector durations vary with S/C spin rate in this mode.

 

2. Sector, Time Command. This command causes only time sectoring to be allowed, regardless of S/C spin rate. The U bits specify the duration of the pseudo-sector generated in this mode. U7...U1 can range from 4F to 59 (hex). This count is measured in terms of the S/C high frequency clock. The value of U7 is 1.1429 sec.; the value of U1 is 0.0179 sec.

 

3. Sector, Auto Command. This command allows the data system to switch between the sun sectoring and time sectoring modes, based on the S/C spin rate. The U bits specify the duration of the pseudo-sector generated when the time sectoring mode is active. The definitions of U7...U1 in the Sector, Time Command apply. These bits must be specified; the format value is not retained.

 

(not in flight units:)

 

4. Internal Calibrator (IC), Auto Command. The IC Auto Command allows the address provided to the IC mux to sequence from 00 to 7F (hex). The address is incremented at the beginning of each format. The A bits specify the starting address. A7...A1 can have the values 00 to 7F. The calibrator addresses are defined in Figure 4.43.

 

5. IC, Fixed Command. This command causes the IC mux address to maintain the value specified by A7..A1 until commanded otherwise. The definitions of the A bits in the IC, Auto Command apply.

 

6. CA PHA, Auto Command. The CA PHA auto command causes the normal priority based processing of the CA PHA schedules to process. The priority schedules for all sectors are initialized at the value P2P1. These are the bits provided to the PHA.

 

7. CA PHA, Fixed Command. This command causes the priority schedule provided to the CA PHA to be maintained at P2P1, for all sectors, until commanded otherwise. All other facets of CA data processing are normal; however, the CA PHA hardware may interpret these bits in another manner.

 

8. CA PHA Reset Command. The CA PHA reset command may be used to reset the PHA if that device should show evidence of having halted operations. The PHA's are reset by hardware when PHA POWER is turned ON.

 

9. Singles, Auto Command. The singles auto command allows the singles mux address to follow the following sequence. Discriminators accessed by each address are defined in an earlier section.

 

Spin pair 1	00
Spin pair 2	01
Spin pair 3	10
Spin pair 4	11
Spin pair 5	00

 

10. Singles, Fixed Command. This command causes the singles mux address to maintain the value S2S1 until commanded otherwise.

 

11. MFSA Pointer Command. The MFSA pointer command sets the MFSA schedule for the next data input cycle, defined in an earlier section, to the value M3M2M1. The schedule sequences normally. During checkout, this command eliminates long waits to calibrate M, F, M', or F' data.

 

12. Powerdown Disable. The powerdown disable command has been eliminated. The goals of this command were in conflict with the concept of a reliable overcurrent protection.

 

13. Powerdown Reset Command. This command resets the latch which had held the output port bits low. After this command is executed, automatic data system operation may set calibration power on, unless it has been commanded off in the interim. All other power bits will remain low until commanded high.

 

14. Cover Commands. Both cover commands must be executed, with both C and D equal to one, to close the telescope covers.

 

15. Output Commands. These commands set the STROBE, ANTI-STROBE, POWER, BIAS SELECT, ANALOG HOUSEKEEPING (AHK) ADDRESS, and SINGLES MUX ADDRESS BITS. They are defined as shown below:

 

 

 

16. Internal Calibration Power Command. When E equals one, power is turned on to the internal calibrator; when E equals zero, power is turned off.

 

4.5.17 Operation

 

The output commands permit single-bit as well as multiple-bit operations. The SET commands cause the parameter(s) specified by those W, X, or Y bits which are ones to be set to one; and those parameters specified by those W, X or Y bits which are zero will be unchanged. The REST commands cause the parameters specified by those W, X or Y bits which are ones to be reset to zero; and those parameters specified by W, X or Y bits which are zeroes will be unchanged.

 

 

Next: Chapter 4.6 Validity Checks of the LAN Data Stream