
19
APPLICATION NOTE #108
Released 9/98
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).