Rockwell Automation 1771-DB BASIC MODULE - Manual (Page 79)

Chapter
Programming Block-Transfers 5
5 -5
The BASIC module is a bi-directional block-transfer module.
Bi-directional means that the module performs both block-transfer-read
and block-transfer-write operations:
Use a BTR instruction to transfer data (1 to 64, 16-bit words) from your
module to the PLC processor’s data table.
Use a BTW instruction to transfer data (1 to 64, 16-bit words) to your
module from the PLC processor’s data table.
The PLC processor sends variable length blocks of data to the module.
You can transfer a maximum of 64 words in and 64 words out per scan.
The module responds with the requested block length of data. The module
has an auxiliary processor dedicated to servicing of the block-transfers to
and from the PLC processor. Use these support routines to provide the
communications link between the PLC processor and BASIC module.
Statement Page
CALL 2 timed-block-transfer-read buffer 12 -2
CALL 3 timed-block-transfer-write buffer 12 -3
CALL 4 set block-transfer-write length 12 -4
CALL 5 set block-transfer-read length 12 -4
CALL 6 block-transfer-write buffer 12 -5
CALL 7 block-transfer-read buffer 12 -5
CALL 120 clear BASIC module input and output buffers 13 -57
Important: Alternate BTR and BTW instructions in ladder logic and
between CALL 7 or CALL 2 and CALL 6 or CALL 3 in your BASIC
program. BTR and BTW instruction enable bits must not be set at the
same time. If you do not, a block-transfer lockup between the PLC
processor and BASIC module may occur.
Block-Transfers and the
BASIC Module