GE PACSystems RX7i, Справочное руководство

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Chapter 6. Serial I/O, SNP & RTU Protocols
GFK-2222AD April 2018 213
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.
Retrieving Data from the Buffer
Data can be retrieved from the buffer using the Read String or Read Bytes function. It is not directly
accessible from the application program.
If data is not retrieved from the buffer in a timely fashion, some characters may be lost.
Example Command Block for the Set Up Input Buffer Function
VALUE
(decimal) VALUE
(hexadecimal)
MEANING
Address 0002 0002 Data block length
A1 0000 0000 NOWAIT mode
A2 0008 0008 Status word memory type (%R)
A3 0000 0000 Status word address minus 1 (%R0001)
A4 0000 0000 Not used
A5 0000 0000 Not used
A6 4301 10CD Setup input buffer command
A7 0064 0040 Buffer length (in words)