Block Transfer
Chapter 10
106
The read and write bits are the enable bits for block transfer modules.
Either one (or both for a bidirectional transfer) is set on in the program
scan when the rung containing the block transfer instruction is true.
The done bit is set on in the I/O scan that the words are transferred,
provided that the transfer was initiated and successfully completed. The
done bit remains on for only one scan.
Block transfer will be requested in each program scan that the read and/or
write bit remains on. The read and/or write bits are turned off when the
rung containing the instruction goes false.
Output Instruction
Block length depends on the kind of module.
Request is made in the program scan.
I/O scan is interrupted for the transfer.
Entire file is transferred in 1 scan.
Done bit remains on for 1 scan after a valid transfer.
Request requires 2 words of the data table.
Key sequence [BLOCK XFER] 0 for write and [BLOCK XFER] 1 for
read.
Misuse and/or inadvertent changes of instruction data can cause run-time
errors when:
The module address is given a non-existent I/O rack number.
A read transfer overruns the file into a processor work area or into user
program by an inadvertent change of the block length code.
To program a block transfer read instruction, press keys [BLOCK XFER] 1
and enter the instruction parameters. To program a block transfer write
instruction, press [BLOCK XFER] 0 and enter the instruction parameters.
An example rung containing a block transfer read instruction and the data
table areas used by the instruction are shown in Figure 10.4. The following
parameters have been entered into the instruction:
Data address 030
Module address 121
Block length 08
File 060
10.2.4
Enable Bit and Done Bit
10.3
Instruction Notes for Block
Transfer Read and Write
Instructions
10.4
Causes of RunTime Errors
10.5
Programming Block
Transfer Read and Write
Instructions
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