!
103
Caution
The IR and SR areas are considered as separate data areas. If an operand has
access to one area, it doesn’t necessarily mean that the same operand will have
access to the other area. The border between the IR and SR areas can, howev-
er, be crossed for a single operand, i.e., the last bit in the IR area may be speci-
fied for an operand that requires more than one word as long as the SR area is
also allowed for that operand.
The
Flags
subsection lists flags that are affected by execution of an instruc-
tion. These flags include the following SR area flags.
Abbreviation
Name
Bit
ER
Instruction Execution Error Flag
25503
CY
Carry Flag
25504
GR
Greater Than Flag
25505
EQ
Equals Flag
25506
LE
Less Than Flag
25507
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 D Error and Arith-
metic Flag Operation
.
When the DM area is specified for an operand, an indirect address can be
used. Indirect DM addressing is specified by placing an asterisk before the
DM:
*
DM.
When an indirect DM address is specified, the designated DM word will con-
tain the address of the DM word that contains the data that will be used as
the operand of the instruction. If, for example,
*
DM 0001 was designated as
the first operand and LR 00 as the second operand of MOV(21), the contents
of DM 0001 was 2222, and DM 2222 contained 5555, the value 5555 would
be moved to LR 00.
MOV(21)
*
DM 0001
LR 00
Word
Content
DM 0000
4C59
DM 0001
2222
DM 0002
F35A
DM 2222
5555
DM 2223
2506
DM 2224
D541
5555 moved
to LR 00.
Indicates
DM 2222.
Indirect
address
When using indirect addressing, the address of the desired word must be in
BCD and it must specify a word within the DM area. In the above example,
the content of
*
DM 0000 would have to be in BCD (between 0000 and 4095
for the C1000H, and between 0000 and 6655 for the C2000H).
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.
Indirect Addressing
Designating Constants
Data Areas, Definer Values, and Flags
Section 5-3
