Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 47)

3–25 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
The values shown in the figure are the maximum allowable values
for position pulses. Bits 14, 15, 16 of the MS position word and the
upper four bits of the LS position word are undefined. They will be
read block transferred to the PC processor as zeros. Bit 17 of the MS
position word is used to indicate a negative position. For example, a
reverse jog to below zero will set bit 17. Bit 17 is zero for a position
between 0 and 999,999 pulses.
All communications between the stepper controller module and the
PC processor data table are controlled by program logic using block
transfer programming. The Mini-PLC-2/15 and PLC-2/30
programmable controllers use block transfer instructions. The
PLC-2/20 uses multiple get instructions for programming block
transfer. Refer to the July 1982 or later edition of the Programming
and Operations Manual for the Mini-PLC-2/15 or PLC-2/30 or the
PLC-3 Programming Manual for a detailed description of block
transfer. These are publications 1772-804, 1772-806 and 1775-801,
respectively.
The remainder of this section describes block transfer concepts
applicable to the stepper controller assembly using block instructions
with the Mini-PLC-2/15 or PLC-2/30 programmable controller.
Block Transfer Overview
The stepper controller is a bidirectional block transfer module.
Bidirectional Block Transfer
Bidirectional block transfer is the performance of alternating read
and write operations. A read operation transfers data from the
stepper controller module to the PC processor data table. A write
operation transfers data from the data table to the stepper controller
module. Two rungs of user program are required, one containing the
block transfer read instruction, the other containing the block transfer
write instruction. The format of the block instructions and the
definitions of terms are shown in Figure 3.16.
Data Address and Module Address
The data address is the block transfer instruction address. It is used
to store the I/O rack address of the stepper controller module
(module address). The module address is stored in BCD by rack,
module group, and slot number and identifies the module’s location
in the I/O rack.
Block Transfer
Programming