TransCore 05531 User Manual

Chapter 6

Communications Protocols

The Encompass 4/4800 Multiprotocol Reader  supports the following communica-
tions protocols:

Basic

Error correcting protocol (ECP)

The following protocol information provides reference information relevant to devel-
oping host software.

Communications are performed using the 7-bit ASCII code with optional parity, thus 
providing easy setup, testing, and diagnostics with standard ASCII terminals and 
serial printers. Parity must be enabled to achieve the specified undetected error rate.

Each message is framed within the start-of-message (som) and end-of-message (eom) 
characters so that the host computer can detect the beginning and end of each mes-
sage. This convention is most important under marginal communications conditions 
during which the host may receive extraneous noise-induced characters between 
reader transmissions. In such instances, the host is capable of ignoring any messages 
that do not conform to the som...eom frame sequence.

Both data mode and command mode require a two-way message interchange is when 
using ECP. This interchange is completed by the message recipient returning a mes-
sage acknowledgement to the message sender.

With ECP, all transmissions require a message. If a message is not received, the sender 
will time out with the same effect as if it had received a negative acknowledgment 
(from the host) or an Error message from the Encompass 4/4800 Multiprotocol 
Reader.

Software (XON/XOFF) flow control is optionally supported. Be careful in the use of 
XON/XOFF since noise-induced characters may be interpreted by the Encompass 4/
4800 Multiprotocol Reader  as the XOFF character, which would suspend reader out-
put without information reaching the host computer. For more information see