Panasonic FP-E Programming Manual page 527

Flag conditions
・Error flag (R9007):
・Error flag (R9008):
How the FIFO buffer is used
The FIFO buffer is a buffer area in which data is stored in the order in which it is written to the buffer, and from
which it is then read out in the stored order, starting from the first data item stored. It is convenient for storing
objects on carrier lines and buffer lines in sequential order.
Usage procedure
The area to be used is defined as the FIFO buffer using the F115 (FIFT) instruction. (This should be done only
once, before reading or writing is done.)
Data should be written using the F117 (FIFW) instruction, and read using the F116 (FIFR) instruction.
Writing data
When data is written, the data items are stored in sequential order, starting from the first data storage area.
The writing pointer indicates the next area to which data is to be written.
If the data storage area becomes full, further data writing is inhibited.
Reading data
When data is read, data is transferred starting from the first data item stored. The reading pointer indicates the
next area from which data is to be read.
An error occurs if an attempt is made to read data when no data has been written to the data storage area.
Example of data storage area
15 0
Reading
pointer ▲ K100
K101
K102
If data is written in the status shown above, the data will be stored in the area indicated by 3. The writing
pointer moves to 4 (the next data item will be written to 4).
If data is read, it will be read from the area indicated by 0. The reading pointer moves to 1 (the next data item
will be read from 1).
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Turns on and stays on when:
Turns on for an instant when:
− The area specified using the index modifier exceeds the limit.
− The size (n) of the FIFO specified by D is n = 0, or when n > 256.
− The number of stored data items of the FIFO > FIFO size (n).
− The final address of the FIFO based on the FIFO size (n) exceeds the area.
− The writing pointer of the FIFO > FIFO size (n).
− The FIFO writing pointer is K256 (H100) or higher after the data has been
written.
0
1
2
3 ▲ Writing pointer
4
High−level Instructions
3 − 263