TransCore 0596465PT15 Manuel D’Utilisation

The host computer resets the anticipated data message sequence 
number to that of the Encompass 4H Reader 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 Encompass 4H Reader sets a user-programmable timeout delay at the time each 
message is transmitted based on command #612NN Set Error Correcting Protocol 
Timeout, where NN = timeout delay. To disable the timeout delay for diagnostic pur-
poses, issue the command #612FF Disable Error Correcting Protocol Timeout.

If the timeout delay expires before the Encompass 4H Reader receives an ACK

or NAK 

message from the host, a logical NAK condition will be declared. If the Encompass 
4H Reader receives a NAK or timeout, the reader retransmits the data message.

When the Encompass 4H Reader receives an ACK message, the system software 
treats the message as having been properly received by the host. The software incre-
ments the sequence number, and advances pointers to the next message in the Encom-
pass 4H Reader’s message queue to prepare for sending the next message.

The host computer may issue command #01 Switch to Command Mode while in data 
mode.

The basic protocol format is as follows:

<som><cmd><eom>

The ECP format is as follows:

<som><seq><cmd><crc><eom>

where

<som>

Start-of-message (ASCII # character)

<seq>

Sequence number generated by the host computer separately 
from that appearing in data messages transmitted by the 
Encompass 4H Reader 

<cmd>

Switch to command mode (ASCII characters 01)

<crc>

CRC value for the message

<eom>

End-of-message character (ASCII CR)