HI-6138_16 Datasheet, PDF (207/254 Pages) Holt Integrated Circuits – Compact Multi-Terminal Device with SPI Host Interface

HI-6138
21.2.7. Programmed BC-Mode Digital Loopback Testing (Off-Line)
For any BC message block, off-line digital loopback self-test can be programmed. The TEST input pin should be logic
0, normal operational state. BC transmission onto the 1553 bus is inhibited for the message, but the digital transmit
encoding and receive decoding signal paths can be checked.
The BC Instruction List in RAM comprises a series of 2-word entries, an instruction Op Code Word followed by a
Parameter Word. While sequencing through the Instruction List, the BC control logic fetches and executes conditional
and unconditional instruction op codes referenced by the “Bus Controller (BC) Instruction List Pointer (0x0034)”. For
executable messages, the Parameter Word following the Op Code Word contains the starting address of a Message
Control/Status Block.
As described in Section “10.4. Bus Controller Message Control / Status Blocks” on page 66, each Message Control/
Status Block begins with a BC Control Word. When Control Word SELFTST bit 6 is set, off-line self-test is enabled,
inhibiting transmission onto the 1553 bus. Instead the output of the bus Manchester II serial encoder is routed directly
to the decoder input for the bus selected by Control Word bit 7 (USEBUSA). A validity check is performed on the
received replica of each transmitted word (sync, encoding, bit count and parity). As received, each word replica is
stored in the Loopback Word location in the Message Control/Status Block. The data value for the final word received
is also checked with the transmitted final word. If any word fails validity check (or if the final word has data mismatch)
test logic sets the LBE (loopback error) bit 8 in the Block Status Word.
After message processing, off-line self-test success or failure can be determined by reading the received Loopback
Word (stored in the Message Control/Status Block if BC is using 16-bit time base) or by reading the LBE (loopback
error) bit 8 in the Block Status Word. (Note: If the BC is using 32-bit time base, the final received loopback word in the
Loopback Word location is overwritten at the end of message post-processing when time tag bits 31:16 are written
there.)
The “BADMSG” BC condition code 0xC is updated based on the outcome of the off-line SELFTST loopback message.
BADMSG is set to logic 1 for Loopback Test error. This permits conditional execution, including jumps or subroutine
calls, based on the outcome of the message having SELFTST asserted in its Control Word.
The BADMSG condition code is also set for Format Error or No Response error, but is not affected by a Status
Set condition. For non-broadcast commands using off-line SELFTST loopback, No Response error always occurs
since the BC message processor expects an RT response. Since BC bus transmission is inhibited, off-line SELFTST
loopback should use broadcast commands. This avoids BADMSG condition codes caused by No Response error.
21.2.8. Continuous BC-Mode Analog Loopback Testing (On-Line)
The BC performs continuous analog loopback on all Bus Controller transmissions when executing normal Message
Control/Status Blocks having off-line SELFTST bit = 0 in each Control Word. The TEST input pin is logic 0, normal
operational state. For each Manchester II word transmitted by the BC, a validity check is performed on the received
replica, checking sync, encoding, bit count and parity. In the Message Control/Status Block, each received word replica
is stored in the Loopback Word location when decoded, overwriting the previous word stored there. The data value for
the final BC word received is also checked for data value. If any word fails validity check (or if the final word has data
mismatch) test logic sets the LBE (loopback error) bit 8 in the Block Status Word. (Note: If the BC is using 32-bit time
base, the final word replica in the Loopback Word location is overwritten at the end of message post-processing when
time tag bits 31:16 are written there.)
The “BADMSG” BC condition code 0xC is updated based on the outcome of continuous BC-mode analog loopback
checking. The BADMSG condition code is set for Loopback Error, Format Error or No Response error, but is not
affected by a Status Set condition. BC analog loopback failure also sets LBE loopback error bit 8 in the Block Status
Word.
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