Siemens SIMATIC S7-1200

Basic instructions
8.6 Move operations
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
283
8.6.8.2
Read and write big and little Endian instructions (SCL)
The S7-1200 CPU provides SCL instructions for reading and writing data in little endian
format and in big endian format. Little endian format means that the byte with the least
significant bit is in the lowest memory address. Big endian format means that the byte with
the most significant bit is in the lowest memory address.
The four SCL instructions for reading and writing data in little endian and big endian format
are as follows:
● READ_LITTLE (Read data in little endian format)
● WRITE_LITTLE (Write data in little endian format)
● READ_BIG (Read data in big endian format)
● WRITE_BIG (Write data in big endian format)
Table 8- 87 Read and write big and little endian instructions
LAD / FBD
SCL
Description
Not available
READ_LITTLE(
src_array:=_variant_in_,
dest_Variable =>_out_,
pos:=_dint_inout)
Reads data from a memory area and writes it to a
single tag in little endian byte format.
Not available
WRITE_LITTLE(
src_variable:=_in_,
dest_array =>_variant_inout_,
pos:=_dint_inout)
Writes data from a single tag to a memory area in little
endian byte format.
Not available
READ_BIG(
src_array:=_variant_in_,
dest_Variable =>_out_,
pos:=_dint_inout)
Reads data from a memory area and writes it to a
single tag in big endian byte format.
Not available
WRITE_BIG(
src_variable:=_in_,
dest_array =>_variant_inout_,
pos:=_dint_inout)
Writes data from a single tag to a memory area in big
endian byte format.
Table 8- 88 Parameters for the READ_LITTLE and READ_BIG instructions
Parameter
Data type
Description
src_array Array of Byte Memory area from which to read
data
dest_Variable Bit strings, integers, floating-point numbers, timers, date and
time, character strings
Destination variable at which to
write data
pos DINT Zero-based position from which to
start reading data from the
src_array input.