3.2 Stopping the software

This section describes how the ACIS instrument software is halted.

3.2.1 BEP Power-Off

This section describes how to power-off the ACIS Digital Processor Assembly (DPA) Back End Processors (BEP).


One method of stopping the ACIS software from running is to power-off the "active" BEP. This can be accomplished by issuing a power-off command or a disable command to the PSMC responsible for the active BEP (see Section 3.1.2 for a discussion on selecting a BEP). The recommended method is to first issue the power-off command, followed by the disable command, however, just issuing the disable command has the same affect.


The following are the commands issued to power-off the BEPs. See Section 3.1.1 for commands to power-on the DPA's BEPs. Also, see Section 3.3.3 for commands needed to enable and power on and off the Detector Electronics Assembly.

Table 8. Power Off Command Sequence
Command Type Description
Power Off Side-A BEP
1DPPSAOF Pulse to PSMC Side-A Power-Off (but don't disable) the PSMC DPA Side-A
1DPPSADS Pulse to PSMC Side-A Disable the PSMC DPA Side-A
Power Off Side-B BEP
1DPPSBOF Pulse to PSMC Side-B Power-Off (but don't disable) the PSMC DPA Side-B
1DPPSBDS Pulse to PSMC Side-B Disable the PSMC DPA Side-B

Engineering Telemetry

For a description of the state of the Engineering telemetry when power is off versus on, refer to Table 4 in Section 3.1.1 .

Science Telemetry

When the power is off on a BEP, the science telemetry is undefined, although experience in the lab indicates that it tends to float to logical `1'.


  1. Lose all loaded parameters and tables

    When a BEP is powered off, it loses all loaded parameter blocks, system configuration values, bad pixel and column maps, patches, Huffman tables and anything else that has been loaded into RAM. When the BEP is re-powered, the default parameter blocks, tables, etc. will be copied from ROM into RAM, and have their respective "as- launched" values (NOTE: This affects power-consumption and the state of the focal plane temperature controller).

  2. DEA may still be running

    Since the DEA and DPA have separate power supplies, the DEA interface boards and video boards will remain powered when the DPA is powered off. Whatever state the DEA is in at the time the DPA is powered down will persist, specifically, the video board power (and clocking state), and the focal plane temperature control settings (including the focal plane bakeout heater state).

3.2.2 Halting the active BEP


Another method of stopping the ACIS software is to halt the active Back End Processor. This is accomplished using a Halt BEP hardware command, or by selecting the other BEP, which throws the current BEP into a reset state (note, that if the other BEP is powered, it will run).


Halting the BEP

1RSETIRT (v=1)  Halt BEP

Selecting BEP B (causing BEP A to be held in a reset state)

1BSELICL (v=1)  Halt Side-A BEP and Select Side-B BEP

Selecting BEP A (causing BEP B to be held in a reset state)

1BSELICL (v=0)  Halt Side-B BEP and Select Side-A BEP

Engineering Telemetry

Selected BEP Bi-level

1STAT4ST  0 - indicates BEP A is selected,
          1 - indicates BEP B is selected

Reset Bi-level

1STAT5ST  0 - indicates selected BEP is not reset (i.e. is running)
          1 - indicates the currently selected BEP is held in reset

Science Telemetry

When the selected BEP is powered up and held in a reset state, it outputs a fill byte, 0xb7, to the software serial digital telemetry channel.


  1. Release of reset causes boot

    Refer to Section, Section, Section 3.1.4 for descriptions of the types of boots which can occur when the BEP's reset is released.

James E. Francis
Last modified: Wed Jan 12 12:32:30 EST