Rockwell Automation 1772-L8_LW_LWP_LX_LXP,D17726.5.8 User Manual - Manual (Page 267)

Block Transfer
Chapter 18
18-2
Figure 18.1
Image Table Byte Relationship versus Module Position
Output image
The lower byte of the I/O image table words are used
when the module is in the lower slot.
17 10 07 00
010
012
017
110
112
117
table word,
lower byte
Input image
table word,
lower byte
Block
transfer
module
I/O rack
Lower
slot
Upper
slot
Data table
10222
Bit numbers
Output image table
Control byte
Input image table
Status byte
The block transfer read or write operation (Figure 18.2) is initiated in the
program scan and completed in the I/O scan as follows:
Program scan – When the rung goes true, the instruction is enabled.
The number of words to be transferred and the read or write bit that
controls the direction of transfer are set by a bit pattern in the control
byte in the output image table.
I/O scan – The processor requests a transfer by sending the output image
table byte of data to the block transfer module during the scan of the
output image table. The module signals the processor that it is ready to
transfer. The processor then interrupts the I/O scan and scans the
timer/counter accumulated area of the data table, looking for the address
of the module that is ready to transfer.