PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 6
GFK-2222AK October 2019
Serial I/O, SNP & RTU Protocols 146
6.2.6.1 Example Command Block for the Initialize Port Function
6.2.6.2 Operating Notes
Remote COMMREQs that are cancelled due to this command executing will return a
COMMREQ status word indicating request cancellation (minor code 12H).
CAUTION
If this COMMREQ is sent when a Write Bytes (4401) COMMREQ is transmitting a string
from a serial port, transmission is halted. The position within the string where the
transmission is halted is indeterminate. In addition, the final character received by the
device to which the CPU is sending is also indeterminate.
6.2.7 Set Up Input Buffer Function (4301)
This function is provided for compatibility with legacy Serial I/O applications. In
PACSystems releases 5.70 and later, the internal input buffer is always set to 2097 bytes.
In earlier PACSystems implementations, the internal input buffer is set to 2K bytes.
The Set Up Input Buffer function returns a success status to the COMMREQ status word,
regardless of the buffer length specified in the command block.
As data is received from the serial port it is placed in the input buffer. If the buffer
becomes full, any additional data received from the serial port is discarded and the
Overflow Error bit in the Port Status word (See Read Port Status Function) is set.
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