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An error occurs if this is executed when the number of stored data
items is 0 or when the reading pointer is equal to the writing pointer.
Reading is only carried out when the reading pointer is not equal to
the writing pointer.
If this is executed when the reading pointer is indicating the final
address in the FIFO buffer (the n defined by the FIFO instruction
minus 1), the reading pointer is set to 0.
Error flags
No.
IEC address
%MX0.900.7
R9007
%MX0.900.8
R9008
This example illustrates the FIFO buffer by incorporating the functions F115_FIFT (see page 483),
Example
F116_FIFR (see page 487) and F117_FIFW (see page 491). The function has been programmed
in ladder diagram (LD) and structured text (ST).
DUT
POU header
All input and output variables used for programming this function have been declared in the POU
header.
Set
If
permanently
the size (n) of the FIFO specified by d1 is
n = 0, or when n > 256.
the number of stored data items of the
FIFO = 0.
the number of stored data items of the
FIFO > FIFO size (n).
the final address of the FIFO based on
for an instant
the FIFO size (n) exceeds the area.
the FIFO reading pointer > FIFO size (n).
the FIFO reading pointer is 256 (16#100)
or higher after the data has been read.
Arithmetic instructions
489
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