CT2555 datasheet(13/36 Pages) AEROFLEX

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

BC OPERATION

Initialization of the CT2553 via a Reset or by

setting the appropriate Configuration Register bits

will result in placing the CT2553 in the BC

operating mode.

MEMORY

CONFIGURATION.

The

user

configures the memory by: (1) writing the start

address of the Descriptor Stack into the Current

Area Stack Point location; (2) loading the fourth

word of each Descriptor Stack Entry (DSE) with

the start location of each message block; and (3)

loading the Message Counter with the total

number of messages to be transmitted. Note that

the Message Count must be written in 1's

compliment.

For

example,

transmit

one

message, load OOFE(H) (See Table 3, BC

Memory Map).

If both map areas A and B are utilized, this

procedure must be performed for each area. Note

that the Stack Pointer and Message Counter

locations are fixed; Message Block locations are

user-defined.

Each message block must be proceeded by a BC

Control Word (See Figure 14). This word informs

the CT2553 as to the format of the message

transfer. Bit 1 of the Control Word defines whether

the following message to RT 31 is to be issued in

Broadcast Mode or whether RT 31 is a unique

terminal. Memory locations must be reserved at

the end of each message for: (1) a Loop Back

Word; (2) RTU Status Word(s); and (3) received

Data words. See Figure 16, BC Message

Formats.

Message blocks may be loaded anywhere in the

non-fixed area of the shared RAM. However, each

data block may not cross a 256 word boundary

(i.e., bit 8 of the starting address of the message

block must match bit 8 of the address of the last

word of the message block).

ADDITIONAL FEATURES. The Configuration

causes the CT2553 to halt operation at the end of

the current message transfer if an error is

detected. In addition, setting the Interrupt Mask

Interrupt (INT) pin with each occurrence of the

respective error, end of message or end of

message frame condition (See Configuration

BC TRANSFER-START SEQUENCE

After setting the CONTROLLER START bit in the

Start/Reset Register, the CT2553 takes the

following actions:

1. Reads the Current Area Stack Pointer for the

address of the Descriptor Stack Entry (DSE).

2. Stores an SOM (Start of Message) flag in the

Block Status word to indicate a transfer

operation in progress.

3. Writes the Time Tag value into the Descriptor

Stack (See Time Tag).

4. Reads the Data Block Address from the fourth

location of the DSE.

5. Starts the MIL-STD-1553 message transfer.

Upon completion of the MIL-STD-1553 message

transfer, the CT2553:

1. Generates an End Of Message (EOM) or Error

(if applicable) interrupt if enabled.

2. Reads the Stack Pointer for the address of the

DSE.

3. Updates the Block Status Word; resets SOM,

sets EOM, and sets any applicable Error bits.

4. Writes the Time Tag value into the Descriptor

Stack (See Time Tag).

5. Increment Pointers: Stack Pointer incremented

by 4 and Message Count incremented by 1.

6. If more messages remain to be sent, a BC End

Of Message (BCEOM) interrupt occurs (if

enabled).

If an error occurs and Stop On Error has been

enabled,

the

CT2553

stops

initiating

Transfer-Start sequences. The Stack Pointer will

point to the next message to be transferred (See

Figure 17).

Table 3 - Typical BC Memory Map

HEX ADDRESS

FUNCTION

Fixed Areas

0100

Stack Pointer A

0101

Message Count A

0104

Stack Pointer B

0105

Message Count B

User Defined Areas

0108-013F

Not Used

0140-017F

Data Block 1

0180-01BF

Data Block 2

01C0-01FF

Data Block 3

•

0F00-0FFF

Descriptor Stack A

0000-00FF

Descriptor Stack B

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