Synchronous block transfer – Rockwell Automation 1771-DB BASIC MODULE User Manual

Page 85

Chapter
Programming Block-Transfers

5 -11

Synchronous Block Transfer

You can use this ladder logic program only with PLC-5 processors to
perform synchronous block transfers. This program assumes that your
application requires a single block-transfer-read (BTR) and
block-transfer-write (BTW) to pass data between the PLC-5 processor and
the BASIC module (transfer of 64 words or less). If transferred data
exceeds 64 words you must program multiple file-to-file moves to move
different data sets to and from block-transfer files.

This example assumes that the BASIC module is in 8 point mode and
resides in group 1, slot 1. Rung 1 is an example of a synchronous
block-transfer-write. When the BASIC module executes a BTW using
CALL 3 or CALL 6, the BASIC module sets bit 01 in the input image
byte. Bit 01 enables the BTW instruction in the ladder logic. When the
block transfer is compete, the BASIC module resets bit 01.

Rung 2 is an example of a synchronous block-transfer-read. When the
BASIC module executes a BTR using CALL 2 or CALL 7, the BASIC
module sets bit 02 in the input image byte. Bit 02 enables the BTR
instruction in the ladder logic. When the block transfer is complete the
BASIC module resets bit 02.

By using this “handshaking” process, the ladder logic enables the block
transfers only when the BASIC module requests them. This process
should help increase the efficiency of the PLC-5 ladder logic programs
when accessing the BASIC module.

BTW

BLOCK TRANSFER WRITE

Rack

Group

Module

N7:15

N7:200

Control Block

Data file

Length

I:001

Rung 3

[END OF FILE]

(EN)

(DN)

(ER)

Continuous

Rung 1

BTR

BLOCK TRANSFER READ