CT2555 datasheet(18/36 Pages) AEROFLEX

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SCDCT2553 REV B 8/6/99 Plainview NY (516) 694-6700

ADDITIONAL FEATURES. Four 1553 Status

Word

flags

can

programmed

via

the

appropriate

Configuration

bits.

addition, setting Interrupt Mask Register bits will

result in a low pulse on the Interrupt (INT) pin

with each occurrence of the respective error or

end of message condition. (See Configuration

THIS RT: Each command appearing on either

1553

Bus

decoded

and

tested

for

Manchester/protocol

errors.

the

CT2553

receives a valid command word containing a

RTU address equivalent to the RTAD0-RTAD4

inputs (pins 10, 9, 50, 49, and 11, respectively),

THIS-RT (pin 55) will be pulsed low. This signal

can be used to identify specific 1553 commands.

This signal is also active in the BC mode.

Command Illegalization (Optional). The CT2553

has the capability to illegalize MIL-STD-1553

mode commands. In addition, valid non-mode

commands can be illegalized based upon the

Command Word subaddress field. An illegal

command is identified by driving the Illegal

Command, ILLCMD (pin 12) input low. The

CT2553

multiplexes

the

Word

Count

and

Subaddress fields (pins SA/MC0 - SA/MC4).

The CT2553 responds to illegalized commands

by transmitting its Status Word with the Message

Error bit set. No data words are transmitted;

received words, however, are placed in the

shared RAM locations indicated by the current

area Look-Up Table.

Upon receipt of a valid mode command, the

CT2553 will output the Command Word-Word

Count field and set the Latched Mode Command

(LMC) output to a logic 1. Upon receipt of a valid

non-mode command, the CT2553 will output the

Command Word-Subaddress field and set the

Latched Mode Command (LMC) output to a

logic 0.

An external PROM can be used for command

illegalization

decoding

the

word

count/subaddress, LMC and Broadcast Received

(BCSTRCV) bits and driving ILLCMD low where

appropriate (See Figure 23).

BUSY BIT. If the user asserts the BUSY bit low

in the Configuration Register, the CT2553 will

respond with a Status Word with the BUSY bit

set. In addition, no data words will be transferred

from the shared RAM as indicated by the

corresponding value in the current area Look-Up

Table. The CT2553 will transfer data associated

with a Receive Command into memory but will

not transmit data out onto the MIL-STD-1553 bus

when busy upon receipt of a Transmit Command.

LMC

SA/MC0-4, T/R

ILLCMD

LATCHED UNTIL NEXT VALID COMMAND WORD RECEIVED

VALID UNTIL NEXT VALID COMMAND WORD RECEIVED

Mode Command Illegalization Timing

SYMBOL

DESCRIPTION

MIN

MAX

UNITS

LMC to ILLCMD latch

250

Figure 23 – Mode Command/Sub-Address Illegalization Timing

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