TransCore 05531 User Manual

The Encompass 4/4800 Multiprotocol Reader  sets a user-programmable timeout 
delay at the time each message is transmitted based on command #612NN Select 
Error Correcting Protocol Timeout

, where NN = timeout delay. To dis-

able the timeout delay for diagnostic purposes, issue the command #612FF Disable 
Error Correcting Protocol Timeout

.

If the timeout delay expires before the Encompass 4/4800 Multiprotocol Reader  
receives an ACK

or NAK message from the host, a logical NAK condition will be 

declared. If the Encompass 4/4800 Multiprotocol Reader  receives a NAK or timeout, 
the reader retransmits the data message.

When the Encompass 4/4800 Multiprotocol Reader  receives an ACK message, the 
system software treats the message as having been properly received by the host. The 
software increments the sequence number, and advances pointers to the next message 
in the Encompass 4/4800 Multiprotocol Reader’s message queue to prepare for send-
ing 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 4/4800 Multiprotocol Reader 

<cmd>

Switch to command mode (ASCII characters 01)

<crc>

CRC value for the message

<eom>

End-of-message character (ASCII CR)

The host computer initiates synchronous communications between the Encompass 4/
4800 Multiprotocol Reader  and the host. The host begins a sequence by issuing a 
command; the Encompass 4/4800 Multiprotocol Reader  responds accordingly.