CT2579 datasheet(9/41 Pages) AEROFLEX

9 / 41 page

APPLICATION NOTE #108

Released 9/98

processor intervention even further, the Command/Status FIFO will only store commands

that have associated data with it.

MESSAGE ILLEGALIZATION

Any message can be illegalized by applying an active low on the NME signal within 600

nSec of the rising edge of NVCR at this time. If NME signal is pulled low, the RT will respond

with a Status word having the Message Error bit set.

One way to implement this function is to place a latching PROM to the T0-T10 data bus. The

PROM would only have to decode 11 bits (5 bits subaddress, 5 bits word count, 1 bit T/R)

and have a one bit output to place a high/low level on the NME input pin. The upper five bits

(T11-T15) are just the Remote Terminal address for the unit which is a constant so no

decode of these bits are necessary. The latching signal for the PROM would be the NVCR

line. The NME pin will be read and acted upon 600 nSec after the rising edge of NVCR. The

NME signal would remain latched and stable until the next rising edge of NVCR.

MIL-STD-1760 FEATURES

To enable the 1760 features checksum validation, the NENCHK line is held low. This

enables the integrated on-chip hardware checksum features. The hardware automatically

checks the incoming message for the correct checksum.

1760 HEADER WORD

The signal NHDR will be an early indicator of the 1760 header word. This headerword will

appear on the T0-15 bus when the NHDR signal is low. The NHDR signal will go low on

every header word (first data word) even if the 1760 checksum circuitry is enabled or not.

NHDR is just an indicator of the first data word on the bus T0-15.

T0-15

NVCR

NME

CMD WD

500 nSec

600 nSec

Max

T0-15

NHDR

1760 HDR WD

500 nSec

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