ACT3492 datasheet(9/49 Pages) AEROFLEX

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SCD3492 REV B 6/26/01 Plainview NY (516) 694-6700

Terminal Flag Bit

This bit is reset to logic zero by a power up initialization or the servicing of a legal mode command to

reset the remote terminal (code 01000). This bit can be set to logic one in the current status register in

four possible ways:

a) If the RX detects any message encoding or content error in the terminals transmission. A loop

test failure, LTFAIL, will be signalled which shall cause the Terminal Flag to be set and the

transmission aborted.

b) If a transmitter timeout occurs while the terminal is transmitting.

c) If a remote terminal self test fails.

d) If there is a parity error in the hard wired address to the RX chip.

This bit, once set, shall be repeatedly set until the detected error condition is known to be no longer

present. The transmission of this bit as a logic one can be inhibited by a legal mode command to inhibit

terminal flag bit (code 00110). Similarly, this inhibit can be removed by a mode command to override

inhibit terminal flag bit (code 00111), a power up initialization or a legal mode command to reset

remote terminal (code 01000).

If ENABLE is held low, then the three options described below are available and are essentially

independent. Any, all, or none may be selected. Also, reporting of faults by the subsystem requires that

SSERR be latched (not pulsed) low until the fault is cleared.

Resetting SSF and TF on Receipt of Valid Commands

If ENABLE is selected and the other three option lines are held high, then the Status Word Register will be

reset on receipt of any valid command with the exception of Transmit Status and Transmit Last Command.

Note that in this mode, the TF will never be seen in the Status Word, and the SSF will only be seen if

SSERR is latched low. Also note that the SSF will not be seen in response to Transmit Status or Transmit

Last Command if the preceding Status Word was clear, regardless of actions taken on the SSERR line after

the clear status transmission.

Status Register Update at Fault Occurrence

If STATUS UPDATE is selected (held low), then the TF or SSF will appear in response to a Transmit Status

or Transmit Last Command issued as the first command after the fault occurs. Any other command (except

as noted in the Preserving the BIT Word section) will reset the TF and SSF. Repeated Transmit Status or

Transmit Last Command immediately following the fault will continue to show the TF and/or SSF in the

Status Word. Note that this behavior may not meet the "letter-of-the-spec" as described in MIL-STD-1553B,

but is considered the "preferred" behavior by some users.

TF and SSF Reporting in the Next Status Word

After the Fault

If NEXT STATUS is selected (held low), then the TF or SSF will appear in response to the very next valid

command after the fault except for Transmit Status or Transmit Last Command. The flag(s) will be reset on

receipt of any valid command following the status transmission with the flag(s) set except for Transmit

Status, Transmit Last Command, or as noted in the following section on Preserving the BIT Word.

Preserving the BIT Word

In order to preserve the Transmitter Timeout Flag, Subsystem Handshake Failure, and Loop Test Failure

Bits in the BIT Word, it is necessary to select BIT DECODE (hold it low). This will prevent resetting those

bits if the Transmit Bit Word Mode Command immediately follows the fault or follows a Transmit Last

Command or Transmit Status immediately following the fault. It will also prevent resetting the TF and SSF

Bits in the Status Word. Any other valid commands will cause those BIT Word Bits and the Status Word Bits

to be reset.

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