CT2577 Datasheet, PDF (19/41 Pages) Aeroflex Circuit Technology – APPLICATION NOTE 108

SELF TEST
The self test feature is an internal and external loop back test for additional verification of
functionality. This is in addition to the Remote Terminal Wraparound circuitry. The difference
is that this test is manual and under subsystem control. The subsystem microprocessor
initiates the self test and the subsequent data word pattern. The subsystem then reads back
the wrapped data word and determines if it is correct. The online self test must be done with
the 1553 data bus quiet.
The self test function is enabled or disabled by writing to certain address locations. Reset
will disable self test.
0 1 00 06
0 1 00 07
0 1 00 08
Enable offline self test and set device status bit 6
Enable online self test and set device status bit 7
Disable self test
When self test is enabled the device is set up as both BC and RT. When self test is disabled
the device will revert back to its previous state.
BASIC OPERATION
The basic operation is for the BC to transmit the message "receive one data word" and for
the RT to receive this message.
If the online self test is selected the message will be transmitted onto the 1553 bus via the
transceivers and be received by the RT via transceivers. The RT will not respond with
Status.
If the offline self test is selected the transceivers will be inhibited and the Manchester
encoder output is routed to the Manchester decoder input.
The status of the device may be obtained by reading from 0 0 00 01. Bit 6 is offline self test
enabled. Bit 7 is online self test enabled.
DETAILED OPERATION
1. Enable self test by writing to either 1 00 06 (offline) or 0 1 00 07 (online).
2. Select required 1553 data bus to be tested by writing to 0 0 00 10 or 0 0 00 18.
3. Write the data word contents required for the self test to the appropriate RAM location ie. For
broadcast message: 2(bcast) 01-1E(subaddress) 00(1 word) or normal receive message: 0(rec)
01-1E(subaddress) 00(1 word).
4. Initiate BC to RT transfer of one data word by writing to address 0 00 00 with a data word content
of 1F or RTaddr 0(rec) 01-1E(subaddress) 01(1 data word). The following automatic sequence is
now initiated:
a) The Command word (data word written to location 0 0 00 00) is processed by the BC protocol,
transferred to the Manchester encoder and transmitted onto the bus (online self test) or to the
Manchester decoder (offline self test).
APPLICATION NOTE #108
19
Released 9/98