6100 MPS-B Programming Manual

INTRODUCTION TO 6100 MPS-B
Message Formats
A station having master status (either the polled tributary
station or 6100 MPS-B after issuing a select sequence) transmits
a message and waits for a reply. The station having slave
status, upon detection of ETX followed by BCC, may send one of
two replies:
1. If the message is accepted, it sends ACK, or a prefix and
ACK.
2. If the message is not accepted, it sends NAK, or a prefix and
NAK.
If the station having master status receives NAK, it will try to
retransmit the message (until the retry count specified for the
line is exhausted) before terminating the message transfer
operation. Note that for Fast Select, the Select sequence and
the message are retransmitted.
If 6100 MPS-B has master status and receives an invalid reply, or
no reply, it sends ENQ to the tributary station. If 6100 MPS-B
receives ENQ in response, it resends the message. It will make
these attempts until it receives a valid response, or until the
retry count specified for the line is exhausted, at which time
the message transfer operation is terminated.
The WRITEREAD buffer Text field is the container for messages
supplied by (transmit request) or given to (receive response)
your application process.
Request Message Format
The request Text field begins with a message control word (MCW)
optionally followed by a sequence header. The message (if any)
follows the sequence header.
The sequence header identifies one or more stations. If the
sequence header is absent, the MCW represents a station index
(the Poll/Select list entry number).
6100 MPS-B permits two different formats for the data supplied by
your application process--free format and ENVOY format.
Free Format. Using this format, your application process may
provide an actual poll/select sequence in the sequence header.
If the sequence header is terminated with ENQ, a poll or select
sequence is indicated; if not, Fast select is indicated.
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