Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 100)

Programming
Chapter 3
3Ć57
Those unfamiliar with block transfer programming techniques should read
the explanation found in the programming and Operation Manual for the
PC processor being used. It is important to under block transfer concepts
before reading this section.
Block Transfer Sequencing
The PID module is designed to sequence the multiple block transfers
required to program the module and actively communicate with the PC
processor. The PID module can prompt a block transfer sequence by
sending to the PC processor the data table address of the first word in the
file to be transferred next in the sequence. A rung in the ladder diagram
program is required to manipulate the file address in the write block
transfer instruction.
The data table address of each of the three data blocks is written to the
PID module in the dynamic block transfer. One word defines the starting
address of each block:
W03 dynamic block start address
W04 loop 1 block start address
W11 loop 2 block start address
The PID module returns to the PC processor the data table address (next
block start address) of the next block to be transferred. The address is the
value in word W59 in the status block. Two rungs are required to perform
the prompting (Figure 3.18). During normal operation rung A gets the
value returned by the PID module in word W59 and puts it in the file
address storage word of the write block transfer instruction. The user
program automatically performs the next block transfer required in the
sequence determined in this manner by the PID module.
Rung B is active only at power-up. If the module is in the power-up mode
and is unprogrammed, it cannot automatically prompt a block transfer.
Instead, the PID module returns the power-up bit W58 B13 = 1 to a data
table storage bit such as 350/13. The power-up bit controls rung B. At
power-up only, rung B forces the write block transfer instruction to
transfer the dynamic block. The dynamic block contains the block start
address for each of the three write blocks. After the PID module receives
this transfer, it can control the sequencing with rung A.