ST52T301 datasheet(94/100 Pages) STMICROELECTRONICS

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SUBO

Subtraction with Offset

Format:

SUBO regi, regj

Operation:

regi <- regi - regj +128

Description:

The contents of the Register File register specified as source are subtracted from the

destination register in the Register File, the value 128 is added to the result that is stored

in the destination register. This operation allows the use of the signed byte considering

the values between 0 and 127 as negative, 128 as 0, and the values between 129 and

255 as positive.

Flags:

Z set if result is zero or if overflow occurs, cleared otherwise.

S set if underflow or overflow, cleared otherwise.

Bytes:

Cycles:

Example:

If the register 4 contains the value 45 and the register 11 contains the value 15, then the

instruction

SUBO 4,11

10010011 0100|1011

causes the register 4 of the Register File to be loaded with the value 158. The value 45

corresponds to -83, the value 11 corresponds to -113; so the operation is equivalent to

perform -83 - (-113) = 30. As a matter of fact the result 158 corresponds to the value 30.

If the register 4 contains the value 50 and the register 11 contains the value 200, the in-

struction causes the register 4 to be loaded with the value 234 (result+256) and the S

flag to be set.

If the register 4 contains the value 200 and the register 11 contains the value 50, the in-

struction causes the register 4 to be loaded with the value 22 (result-256) and the S and

Z flags to be set.

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ST52T301/E301

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