25
These clock pulse bits are often used with counter instructions to create tim-
ers. Refer to
5–11 Timer and Counter Instructions
for an example of this.
Pulse width 0.1 s 0.2 s 1.0 s
Bit 1900 1901 1902
SR 1900
0.1-s clock pulse
0.1 s
.05 s .05 s
SR 1901
0.2-s clock pulse
0.2 s
0.1 s 0.1 s
SR 1902
1.0-s clock pulse
1.0 s
0.5 s 0.5 s
Caution:
Because the 0.1-second clock
pulse bit has an ON time of 50 ms,
the CPU may not be able to accu-
rately read the pulses if program
execution time is too long.
3–4–5 Error Flag ER
SR 1903 turns ON when the results of an arithmetic operation is not output in
BCD or the value of the BIN data processed by the BIN to BCD or BCD to
BIN conversion instruction exceeds 9999. When the ER Flag is ON the cur-
rent instruction is not executed.
3–4–6 Always OFF and Always ON Flags
SR 1811, SR 1812 and SR 1814 are always OFF and AR 1813 is always ON.
By connecting these bits to external indicating devices such as a LED they
can be used to monitor the PC’s operating status.
3–4–7 First Scan Flag
SR 1815 turns ON when program execution starts and turns OFF after one
scan.
3–4–8 Arithmetic Flags
The following flags are used in data shifting, arithmetic calculation, and com-
parison instructions. They are generally referred to only by their two-letter
abbreviations. These flags are all reset when END is executed, and therefore
cannot be monitored from a Programming Device.
Refer to
5–12 Data Shifting
,
5–14 Data Comparison
and
5–16 BCD Calcula-
tions
for details.
SR 1904 turns ON when there is a carry in the result of an arithmetic opera-
tion. The content of CY is also used in some arithmetic operations, e.g., it is
added or subtracted along with other operands. This flag can be set and
cleared from the program using the STC and CLC instructions. Use CLC be-
fore any instruction using CY unless the current content of CY is required.
SR 1905 turns ON when the result of a comparison shows the second of two
4-digit operands to be greater than the first.
Carry Flag, CY
Greater Than Flag, GR
SR Area Section 3–4
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