6100 MPS-B Programming Manual

INTRODUCTION TO 6100 MPS-B

Error Handling

The following means of handling error conditions have been

mentioned in this section:

• Block Check Character (BCC)

• Retries

• Timeouts

• Negative Acknowledgements

Block Check Character

The Block Check Character (BCC) is the result of a running

computation during data transmission. It is used by the

communicating stations for error control. The computation begins

with the character following the STX (or SOH--see "Message

Formats" in this section) and proceeds through the final ETX.

The station sending the message computes and transmits the block

check sequence; the receiving station performs the same

computation and compares its result to the received sequence. If

the sender and receiver have the same results, the message is

assumed to be error-free.

NOTE

You need not be concerned about the details of BCC compu-

tation. 6100 MPS-B supplies the BCC sequence. It is not

visible to the application process.

Retries

Operations are subject to transmission errors such as

Longitudinal Redundancy Check (LRC) parity errors, nonresponding

terminals, and invalid responses from terminals. When errors of

these types are encountered, 6100 MPS-B, on behalf of the

application process, retries the requested operation.

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