Chapter 6. Serial I/O, SNP & RTU ProtocolsGFK-2222AD April 2018 2136.2.7 Set Up Input Buffer Function (4301)This function is provided for compatibility with legacy Serial I/O applications. In PACSystems releases5.70 and later, the internal input buffer is always set to 2097 bytes. In earlier PACSystemsimplementations, 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 ofthe 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, anyadditional data received from the serial port is discarded and the Overflow Error bit in the Port Statusword (See Read Port Status Function) is set.Retrieving Data from the BufferData can be retrieved from the buffer using the Read String or Read Bytes function. It is not directlyaccessible 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 FunctionVALUE(decimal)VALUE(hexadecimal) MEANINGAddress 0002 0002 Data block lengthAddress +1 0000 0000 NOWAIT modeAddress +2 0008 0008 Status word memory type (%R)Address +3 0000 0000 Status word address minus 1 (%R0001)Address +4 0000 0000 Not usedAddress +5 0000 0000 Not usedAddress +6 4301 10CD Setup input buffer commandAddress +7 0064 0040 Buffer length (in words)
