GE PACSystems RX7i, Reference Manual

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Chapter 6. Serial I/O, SNP & RTU Protocols
GFK-2222AD April 2018 215
6.2.9 Read Port Status Function (4303)
This function returns the current status of the port. The following events can be detected:
1.
A read request was initiated previously and the required number of characters has now been
received or the specified time-out has elapsed.
2. A write request was initiated previously and transmission of the specified number of characters is
complete or a time-out has elapsed.
The status returned by the function indicates the event or events that have completed. More than one
condition can occur simultaneously, if both a read and a write were initiated previously.
Example Command Block for the Read Port Status Function
VALUE
(decimal) VALUE
(hexadecimal) MEANING
Address 0003 0003 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 4303 10CF Read port status command
A7 0076 004C Port status memory type (%M)
A8 0101 0065 Port status memory offset (%M101)
Port Status
The port status consists of a status word and the number of characters in the input buffer that have not
been retrieved by the application (characters which have been received and are available).
word 1 Port status word (see below)
word 2 Characters available in the input buffer