TransCore 05716 Manuel D’Utilisation

message was received in error, and transmits a NAK message 
response.

<eom>

End-of-message characters (ASCII CR and LF). The system 
includes both a carriage return (CR) and line feed (LF) to 
facilitate the use of terminals and printers.

If the host receives a <som> character in the middle of a data 
message, the message in progress is aborted. The assumption is 
that an <eom> was lost and the MPRR is in the process of 
retransmitting the previous message.

With ECP, the host computer responds to all data message transmissions from the 
MPRR using the following acknowledgment or negative acknowledgment response 
format.

<som><seq><ack/nak><crc><eom>

where

<som>

Start-of-message (ASCII # character)

<seq>

An echo of the sequence number received from the MPRR. The 
sequence number should correspond to the data message that is 
being positively or negatively acknowledged by the host. If the 
MPRR receives an ACK message with the incorrect sequence 
number, the data message is retransmitted.

The host computer resets the anticipated data message sequence 
number to that of the MPRR before communications can resume 
without error.

<ack/nak>

ASCII @ character for ACK response; ASCII ? character for NAK 
response

<crc>

CRC value for the message

<eom>

End-of-message character (ASCII CR)

The MPRR sets a user-programmable timeout delay at the time each message is trans-
mitted based on command #612NN Set Error Correcting Protocol Timeout, where NN 
= timeout delay. To disable the timeout delay for diagnostic purposes, issue the com-
mand #612FF Disable Error Correcting Protocol Timeout.

If the timeout delay expires before the MPRR receives an ACK

or NAK message from 

the host, a logical NAK condition will be declared. If the MPRR receives a NAK or 
timeout, the reader retransmits the data message.

When the MPRR receives an ACK message, the system software treats the message as 
having been properly received by the host. The software increments the sequence