Rockwell-automation 1771-DB Basic Module User Manual - Series A Manual de usuario descargar pdf (Pagina 142)

Programming

Chapter 6

6–10

1. The block lengths PUSHed for CALLs 4 and 5 must equal the

corresponding

lengths on your BTW/BTR instructions in the processor

2. If

a BTW appears first in your ladder logic, put CALLs 3 or 6 first in your

BASIC

program. If a

BTR appears first in your ladder logic, put CALLs

2 or 7 first in your BASIC program.

3. Set the PLC-5 block-transfer-write timeout bit (block-transfer control

block,

word 0 bit 8) to eliminate excessive PLC-5 scan times. When the

timeout bit sets, the processor attempts two DB block-transfers before

generating

a block-transfer error

. The error condition resets the enable bit

and restarts the block-transfer in our program example, figure 6.7.

4. If your application requires bidirectional block-transfers, you can use

CALL 6 or 3 and CALL 7 or 2 as necessary if:

you use an equal number of each type.

you alternate their use (e.g. CALL 6, CALL 7, CALL 6, CALL

7)You can put the calls anywhere in the program. They can occur

at any time interval.

5. If your application requires a one way block-transfer (all

write-block-transfers

or all read-block-transfers, use only the associated

CALLs (4, and 3 or 6; 5, and 2 or 7).

6.6.

Block-T

ransfer

Programming Tips

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Rockwell-automation 1771-DB Basic Module User Manual - Series A Manual de usuario Pagina 142