Omron SYSMAC CJ - REFERENCE MANUAL 08-2008 Reference Manual page 786

Table Data Processing Instructions
Description
Offset value
C
Flags
Precautions
Examples
746
Area
Index Registers
Indirect addressing
using Index Registers
SREAD(639) reads the data from the address specified by the stack pointer
(TB+3 and TB+2) minus the offset value in C. SREAD(639) does not change
the data in the stack or the stack pointer.
Stack
TB
TB+1
TB+2
TB+3
TB+4
Pointer
Last word
in stack
Reads the data (A) without
changing the stack pointer.
SREAD(639) can be used to read the data for an item currently on a conveyor.
The position of the desired item is simply the number of items back (the offset
value) from the most recent item added to the conveyor.
Name
Error Flag
Equals Flag
The stack must be defined in advance with SSET(630).
The address in the stack pointer must be greater than the PLC memory
address of the beginning of the data region (TB+4). An error will occur if the
stack pointer is less than the PLC memory address of TB+4, i.e., if a stack
underflow error occurs.
When CIO 000000 is ON in the following example, SREAD(639) reads the
data in the specified word in the stack starting at D00000 and outputs the data
to D00100. In this case, the stack pointer indicates D00007 and the offset
value is 3, so the data is read from D00004.
TB
---
,IR0 to ,IR15
–2048 to +2047 ,IR0 to –2048 to +2047 ,IR15
DR0 to DR15, IR0 to IR15
,IR0+(++) to ,IR15+(++)
,–(– –)IR0 to, –(– –)IR15
PLC memory
address
n
m
The data (A) is
A
not changed.
B
C
m
n
D
Reads the data (A) in the specified
word and outputs that data to D.
The address of the desired word is
calculated by subtracting the offset
value from the stack pointer address.
Label
ER ON if the specified read location is not within the stack
area.
ON if the offset value specified in C is 0 or greater than
the maximum data region size (FFFB hex).
OFF in all other cases.
= ON if the output data in D is 0000.
OFF in all other cases.
Section 3-17
C
A
Operation
D