What is the function of the BU-65178 Mini-ACE™’s SSFLAG*/EXT_TRIG input?
A. For the BU-65178 RT Mini-ACE™, the only function of the SSFLAG*/EXT_TRIG input signal is as a SSFLAG* (Subsystem Flag) input. The “EXT_TRIG” function is not applicable to the BU-65178 RT. EXT_TRIG is a BC and Monitor function that is only applicable to the BU-61588 Mini-ACE™ BC/RT/MT, and the BU-61688/89 Mini-ACE™ Plus BC/RT/MT. If SSFLAG* is connected to logic “0”, this will cause the Subsystem Flag bit in the RT Status word to be set to logic “1”. If SSFLAG* is connected to logic “1”, the value of Subsystem Flag will be determined by the software programming of Configuration Register #1. Therefore, if you don’t intend to use this function, I recommend that you hardwire SSFLAG*/EXT_TRIG to logic “1”. One use of the SSFLAG* input is to provide a hardware mechanism for a processor watchdog timer to be able to signal to the 1553 RT that it has timed out (i.e., that the processor has hung up). Q. We have connected the Mini-ACE™’s SSFLAG* input pin to a processor watchdog timer circuit.
