Appendix C
Memory Areas
577
Word(s)
Page
Read/
write
Function
Bit(s)
SR 253
00 to 07
FAL Error Code
The error code (a 2-digit number) is stored here when an error occurs. The
FAL number is stored here when FAL(06) or FALS(07) is executed. This word
is reset (to 00) by executing a FAL 00 instruction or by clearing the error from
a Programming Device.
Read-
only
385
08
Battery Error Flag
Turns ON when the CPU Unit backup battery’s voltage is too low.
---
09
Cycle Time Overrun Flag
Turns ON when a cycle time overrun occurs (i.e., when the cycle time ex-
ceeds 100 ms).
---
10,11
Not used.
12
Changing RS-232C Setup Flag
Turns ON when the RS-232C port’s settings are being changed.
Read/
write
---
13
Always ON Flag
Read-
l
---
14
Always OFF Flag
only
---
15
First Cycle Flag
Turns ON for 1 cycle at the start of operation.
---
SR 254
00
1-minute clock pulse (30 seconds ON; 30 seconds OFF)
---
01
0.02-second clock pulse (0.01 second ON; 0.01 second OFF)
---
02
Negative (N) Flag
---
03
Not used.
04
Overflow (OF) Flag
Turns ON when an overflow occurs in a signed binary calculation.
Read-
only
---
05
Underflow (UF) Flag
Turns ON when an underflow occurs in a signed binary calculation.
o y
---
06
Differential Monitor Complete Flag
Turns ON when differential monitoring is completed.
159
07
STEP(08) Execution Flag
Turns ON for 1 cycle only at the start of process based on STEP(08).
385
08 to 15
Not used.
SR 255
00
0.1-second clock pulse (0.05 second ON; 0.05 second OFF)
Read-
l
---
01
0.2-second clock pulse (0.1 second ON; 0.1 second OFF)
only
---
02
1.0-second clock pulse (0.5 second ON; 0.5 second OFF)
---
03
Instruction Execution Error (ER) Flag
Turns ON when an error occurs during execution of an instruction.
---
04
Carry (CY) Flag
Turns ON when there is a carry in the results of an instruction execution.
---
05
Greater Than (GR) Flag
Turns ON when the result of a comparison operation is “greater.”
---
06
Equals (EQ) Flag
Turns ON when the result of a comparison operation is “equal,” or when the
result of an instruction execution is 0.
---
07
Less Than (LE) Flag
Turns ON when the result of a comparison operation is “less.”
---
08 to 15
Not used.
Note
DM 6601 in the PC Setup can be set to maintain the previous status of the Forced Status Hold Bit
(SR 25211) and the I/O Hold Bit (SR 25212) when power is turned OFF. Refer to
1-1-3 CPM2A/CPM2C PC
Setup Settings
for details on the PC Setup.
