72
Abbreviation Name Bit
ER Instruction Execution Error Flag 0311
CY Carry Flag 0312
LE Less Than Flag 0313
EQ Equals Flag 0314
GR Greater Than Flag 0315
ER is the flag most commonly used for monitoring an instruction’s execution.
When ER goes ON, it indicates that an error has occurred in attempting to
execute the current instruction. The Flags subsection of each instruction lists
possible reasons for ER being ON. ER will turn ON if operands are not en-
tered correctly. Instructions are not executed when ER is ON. A table of in-
structions and the flags they affect is provided in Appendix E Error and Arith-
metic Flag Operation.
When the DR area is specified for an operand, an indirect address can be
used. Indirect DR addressing is specified by placing an asterisk before the
DR: *DR.
When an indirect DR address is specified, the designated DR word will con-
tain the address of the DR word that contains the data that will be used as
the operand of the instruction. If, for example, *DR 01 was designated as the
first operand and LR 00 as the second operand of MOV(30), the contents of
DR 01 was 0006, and DR 06 contained 5555, the value 5555 would be
moved to LR 00.
MOV(30)
*DR 01
LR 00
Word Content
DR 00 4C23
DR 01 0006
DR 02 F3A3
DR 06 5555
DR 07 2255
DR 08 D1C5
5555
moved to
LR 00.
Indicates
DR 06.
Indirect
address
When using indirect addressing, the address of the desired word must be in
BCD and it must specify a word within the DR area. In the above example,
the content of *DR 00 would have to be in BCD and between 0000 and
1515.
Although data area addresses are most often given as operands, many oper-
ands and all definers are input as constants. The available value range for a
given definer or operand depends on the particular instruction that uses it.
Constants must also be entered in the form required by the instruction, i.e., in
BCD or in hexadecimal.
3-7-4 Coding Right-hand Instructions
Writing mnemonic code for ladder instructions has already been described
for ladder instructions. Converting the information in the ladder diagram sym-
bol for all other instructions follows the same pattern, as described below,
and is not specified for each instruction individually.
The first word of any instruction defines the instruction and provides any de-
finers. If the instruction requires only a signal bit operand with no definer, the
Indirect Addressing
Designating Constants
Instruction Set Section 3-7
To Next Page
Loading...
Need help?
General
