12.4.12 Read Bytes Function (4402)
This function causes one or more characters to be read from the specified port. The
characters are read from the internal input buffer and placed in the specified input data
area.
The function returns both the number of characters retrieved and the number of
unprocessed characters still in the input buffer. If zero characters of input are requested,
only the number of unprocessed characters in the input buffer is returned.
If insufficient characters are available to satisfy the request and a non-zero value is
specified for the number of characters to read, the status of the operation is not complete
until either sufficient characters have been received or the time-out interval expires. In
either of those conditions, the port status indicates the reason for completion of the read
operation. The status word is not updated until the read operation is complete (either due
to timeout or when all the data has been received).
If the time-out interval is set to zero, the COMMREQ remains pending until it has
received the requested amount of data, or until it is cancelled.
If this COMMREQ fails for any reason, no data is returned to the buffer. Any data that
was already in the buffer remains, and can be retrieved with a subsequent read request.
12.4.12.1 Example Command Block for the Read Bytes
Function
VALUE
(decimal)
VALUE
(hexadeci-
mal)
MEANING
address 0005 0005
Data block length
address +1 0000 0000 NOWAIT mode
address +2 0008 0008
Status word memory type (%R)
address +3 0000 0000
Status word address minus 1 (%R0001)
address +4 0000 0000 Not used
address +5 0000 0000 Not used
address +6 4402 1132
Read bytes command
address +7 0030 001E
Read time-out (30 seconds)
address +8 0005 0005
Number of bytes to read
address +9 0008 0008
Input data memory type (%R).
address +10 0100 0064
Input data memory address (%R0100)
246 GFK-1503E VersaMax PLC User Manual
For public disclosure
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