Basic Instructions
2 − 139
Explanation of example
Compares the contents of data registers (DT1, DT0) with the data registers (DT101, DT100).
If (DT1, DT0) = (DT101, DT100), the external output relay Y30 goes on and if (DT1, DT0) > (DT101, DT100),
the external output relay Y31 goes on.
Description
Compares the double word data specified by S1 and S1+1 with the double word data specified by S2 and
S2+1 according to the comparison condition.
The STD instruction initiates a logical operation as the liaison contact when the comparison result is a
specified status (=, <, >, etc.).
The result of the comparison operation is as follows:
Comparison
Condition
instruction
(S1+1, S1) <
(S2+2, S2)
(S1+1, S1) =
(S2+2, S2)
(S1+1, S1) >
(S2+2, S2)
STD= off on off
STD<> on off on
STD> off off on
STD>= off on on
STD< on off off
STD<= on on off
When processing 32-bit data, the higher 16-bit areas (S1+1, S2+1) are automatically determined once the
lower 16-bit areas (S1, S2) are specified.
S1S1+1
S2S2+1
The specified data area and the following data area are handled
together as 32−bit data.
Comparison
Precautions concerning usage
The start comparison instructions STD =, STD <>, STD >, STD >=, STD <, and STD <= are programmed from
the bus line.
If mixed with BCD or other type of data, the value will be regarded as negative when the most significant bit is 1
and a correct comparison may not be obtained. In this case, use an F83 (DBIN) instruction or similar
instruction to change the data to binary data before making the comparison.
Flag conditions
・Error flag (R9007): Turns on and stays on when the area specified using the index modifier
exceeds the limit.
・Error flag (R9008): Turns on for an instant when the area specified using the index modifier
exceeds the limit.
< > indicates
>= indicates
<= indicates
To Next Page