CT2579 datasheet(19/41 Pages) AEROFLEX

19 / 41 page

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

Enable offline self test and set device status bit 6

0 1 00 07

Enable online self test and set device status bit 7

0 1 00 08

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).

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).

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