12Read Bytes Function (4402) - GE VersaMax PLC User Manual

address
address +1
address +2
address +3
address +4
address +5
address +6
address +7
address +8
address +9
address +10
246 GFK-1503E
For public disclosure
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
VALUE
(hexadeci-
(decimal)
mal)
0005 0005
0000 0000
0008 0008
0000 0000
0000 0000
0000 0000
4402 1132
0030 001E
0005 0005
0008 0008
0100 0064
MEANING
Data block length
NOWAIT mode
Status word memory type (%R)
Status word address minus 1 (%R0001)
Not used
Not used
Read bytes command
Read time-out (30 seconds)
Number of bytes to read
Input data memory type (%R).
Input data memory address (%R0100)
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