Siemens Simatic S7-300 Service Manual download pdf (Page 169)

Statement List (STL) for S7-300 and S7-400 Programming

A5E00706960-01

11-1

11 Shift and Rotate Instructions

11.1 Shift Instructions

11.1.1 Overview of Shift Instructions

Description

You can use the Shift instructions to move the contents of the low word of

accumulator 1 or the contents of the whole accumulator bit by bit to the left or the

right (see also CPU Registers). Shifting by n bits to the left multiplies the contents of

the accumulator by ”2

”; shifting by n bits to the right divides the contents of the

accumulator by ”2

”. For example, if you shift the binary equivalent of the decimal

value 3 to the left by 3 bits, you end up with the binary equivalent of the decimal value

24 in the accumulator. If you shift the binary equivalent of the decimal value 16 to the

right by 2 bits, you end up with the binary equivalent of the decimal value 4 in the

accumulator.

The number that follows the shift instruction or a value in the low byte of the low word

of accumulator 2 indicates the number of bits by which to shift. The bit places that are

vacated by the shift instruction are either filled with zeros or with the signal state of

the sign bit (a 0 stands for positive and a 1 stands for negative). The bit that is shifted

last is loaded into the CC 1 bit of the status word. The CC 0 and OV bits of the status

word are reset to 0. You can use jump instructions to evaluate the CC 1 bit. The shift

operations are unconditional, that is, their execution does not depend on any special

conditions. They do not affect the result of logic operation.

The following Shift instructions are available:

• SSI Shift Sign Integer (16-Bit)

• SSD Shift Sign Double Integer (32-Bit)

• SLW Shift Left Word (16-Bit)

• SRW Shift Right Word (16-Bit)

• SLD Shift Left Double Word (32-Bit)

• SRD Shift Right Double Word (32-Bit)

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Siemens Simatic S7-300 Service Manual Page 169