CT2555 datasheet(16/36 Pages) AEROFLEX

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

RTU OPERATION

The RTU mode is selected by resetting the

CT2553 and setting the appropriate bits in the

Configuration Register.

RTU MEMORY CONFIGURATION. The user

configures the memory by:

1. Writing the start address of the Descriptor

Stack into the Stack Pointer location and

2. Setting up the Look-Up Table as described

below.

If both map areas (A and B) are utilized, this

procedure must be performed for each area. Note

that the Stack Pointer and Look-Up Table

locations are fixed; Data Block(s) locations are

user-defined. Message blocks may be loaded

anywhere in the non-fixed areas 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). An example of a typical RTU Memory Map

is given in Table 4. Figure 19 shows the RTU

Initialization steps.

RTU LOOK-UP TABLE. The RTU mode uses a

Look-Up Table in order to map the Data Blocks

based upon incoming 1553 Command Words.

The CT2553 uses the T/R and Subaddress fields

to address the Look-Up Table. Each Look-Up

Table (A and B) location contains a user-defined

Data Block Pointer to an associated Data Block

(See Figures 20 and 21).

Note: The Data Block and Stack Pointers are

maintained

internally

using

8-BIT-REGISTER for the HIGH BYTE and an

8-BIT COUNTER for the LOW BYTE; the high

byte remains constant (user value) while the low

byte will wrap around from FF(H) to 00(H). For

example: a current Pointer value of 10 FF(H)

will increment to 10 00(H) and not 11 00(H).

The first 32 words of the Look-Up Table are

reserved for Data Blocks associated with Receive

Commands (T/R bit = 0). The remaining 32 words

are reserved for Data Blocks associated with

Transmit Commands (T/R bit = 1).

Mode Commands with data are mapped in the

same

manner

non-mode

commands.

Synchronize With Data command maps to the

first or thirty-second Table entry (depending upon

subaddress: all 0's or all 1's), while a Transmit

Vector Word command points to the thirty-third or

sixty-fourth entry.

Table 4 – Typical RTU Memory Map

HEX ADDRESS

FUNCTION

Fixed Areas

0100

Descriptor Stack Pointer A

0101

Reserved

0104

Descriptor Stack Pointer B

0105

Reserved

0108-013F

Spare

0140-017F

Look-Up Table A

01C0-01FF

Look-Up Table B

User Defined Areas

0180-019F

Data Block 1

01A0-01BF

Data Block 2

0200-021F

Data Block 3

•

0EE0-0EFF

Data Block 107

0000-00FF

Descriptor Stack A

0F00-0FFF

Descriptor Stack B

START

ISSUE RESET COMMAND

INITIALIZE STACK POINTER

SET UP DATA BLOCKS

WAIT FOR 1553 COMMAND

SET UP LOOK-UP TABLE(S)

DATA BLOCK ASSIGNMENTS

Figure 19 – RTU Initialization

INITIALIZE INTERRUPT

MASK REGISTER

SET CONFIGURATION

START REGISTER

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