6100 MPS-B Programming Manual

INTRODUCTION TO 6100 MPS-B
Error Handling
A retry count value is defined in SYSGEN that specifies the
maximum number of times that 6100 MPS-B will retry an operation.
This value can be altered subsequent to system generation through
a SET CONFIGURATION request, a STATION CONTROL Alter Line request
(see Section 3), or a CMI ALTER command. If the error condition
persists after the operation has been retried the maximum number
of times, an error condition status code is returned to the
application process in the WRITEREAD buffer.
Timeouts
6100 MPS-B uses timeouts to detect an error condition. When a
timeout condition is encountered, 6100 MPS-B, on behalf of the
application process, retries the requested operation.
A timeout value is defined in SYSGEN that specifies the maximum
amount of time that 6100 MPS-B will wait for an acknowledgement
to a request. This value can be subsequently altered through a
SET CONFIGURATION request, a STATION CONTROL Alter Line request
(see Section 3), or a CMI ALTER command.
During a write operation, the timeout value determines the period
of time following the selection of a station that 6100 MPS-B will
wait for an acknowledgement. During a read operation, the
timeout period determines how long 6100 MPS-B will wait for an
acknowledgement from a polled station.
An operation that exceeds the timeout value is retried until the
retry count value (described above) is exhausted. Then, an error
condition status code is returned to the application process in
the WRITEREAD buffer.
Negative Acknowledgements
During data transmission, certain error conditions occur from
time to time. The occurrence of an error causes 6100 MPS-B to
attempt recovery on behalf of your application process. Examples
of these error conditions are: a block check character (BCC)
error when receiving data, a NAK received when transmitting data,
or an incorrect ACK received when transmitting data. 6100 MPS-B
uses the negative acknowledgement (NAK) to cause retransmission
of data.
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