CT2555 datasheet(17/36 Pages) AEROFLEX

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

RTU MESSAGE BLOCK TRANSFER SEQUENCE

RTU

message

transfer

operations

begin

automatically upon receipt of a valid command

word from the 1553 bus. A message transfer

takes the form of an RTU Start Of Message

(SOM) cycle followed by the 1553 Message

Transfer Cycle and an RTU End Of Message

(EOM) cycle (See Figure 22).

During the RTU SOM cycle, the CT2553 the

following actions:

1. Loads the 1553 command word.

2. Reads the current area Stack Pointer to get the

address of the current Descriptor Stack Entry

(DSE).

3. Stores an SOM flag into the Block Status Word

to indicate a transfer in progress.

4. Writes the Time Tag value into the the

Descriptor Stack.

5. Stores the Command Word received.

6. Reads the associated Data Block Address from

the (current area) Look-Up Table.

The MESSAGE TRANSFER CYCLE refers to the

actual transfer of the 1553 message under control

of the CT2553. The CT2553 transfers data to and

from the memory on a word-by-word basis.

Upon completion of the message transfer, the

CT2553 executes an RTU End Of Message

(EOM) cycle during which the CT2553:

1. Generates an EOM or Error interrupt (if

enabled).

2. Updates the Block Status Word: clears SOM,

sets EOM, and any appropriate error bits.

3. Writes the Time Tag value into the Descriptor

Stack.

4. Increments the Stack Pointer by 4.

Figure 22 – RTU Message Transfer

Operation

MESSAGE COMPLETE

GENERATE EOM INTERRUPT AND

CONDITION DETECTED

ERROR INTERRUPT IF ERROR

INCREMENT STACK POINTER

BY FOUR

UPDATE BLOCK STATUS WORD

AND TIME TAG

TRANSFER DATA TO/FROM

1553 INTERFACE DEVICE

READ LOOK-UP TABLE USING

AREA BIT B/A

T/R SUBADDRESS CURRENT

UPDATE DESCRIPTOR STACK

TAG AND COMMAND WORD

BLOCK STATUS WORD, TIME

READ STACK POINTER

1553 COMMAND WORD

RECEIVED

YES

WAIT FOR NEXT

1553 COMMAND

7 6 5 4 3 2 1 0

0 0 0 0 0 0 0 1

CURRENT AREA B/A

T/R (from command word)

SUB-ADDRESS (command word)

Figure 20 – RTU Look-Up Address

RECEIVED COMMAND WORDS

DATA BLOCK

T/R

SUBADD

WORD

COUNT

LOOK-UP

TABLE (A)

ADDRESS

DATA BLOCK

00000

XXXXX

0140

USER DEFINED

00001

XXXXX

0141

USER DEFINED

00010

XXXXX

0142

USER DEFINED

64 LOCATIONS

11110

XXXXX

017E

USER DEFINED

11111

XXXXX

017F

USER DEFINED

Figure 21 – Look-Up Table Example

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