TransCore 0596465PT15 Manuel D’Utilisation

With basic protocol, messages sent to and from the Encompass 4H Reader and the 
host are transmitted without error checking. For each host transmission, the Encom-
pass 4H Reader returns a Done

or Error

message to the host.

When the host computer is physically close to the Encompass 4H Reader and no 
sources of interference exist, the basic protocol provides reliable communications.

The host must be ready to receive reader-transmitted messages because in basic proto-
col the Encompass 4H Reader does not wait for the host to acknowledge a message 
before transmitting the next message. If necessary, the host may halt reader transmis-
sions by using software or hardware flow control. Refer to Chapter 

 for flow control 

information.

When the quality of data communications is imperative or may be suspect, you can 
invoke ECP to ensure the integrity of data transmitted between the Encompass 4H 
Reader and the host. 

Wiegand output is automatically disabled when the reader is put into ECP mode.

Error correction is accomplished with the use of a cyclic redundancy check (CRC) 
value that is based on the message data. The originator (reader or host) calculates the 
CRC value of a message and includes it in the transmitted message.

The recipient (reader or host) also calculates a CRC value for the received message. If 
the transmitted message data is correct, the CRC value calculated by the recipient will 
agree with the CRC value calculated by the originator. If the CRC values do not agree, 
the recipient rejects the message.

Message sequence numbers are also included when using ECP. These sequence num-
bers are checked to determine if the message received has the correct sequence num-
ber; if not, the recipient rejects the message.

Since the seven-bit ASCII code is used and there are eight data bits per character, the 
eighth bit can optionally be used to support parity. Where parity is selected, the CRC 
value calculation includes the parity of each character in the calculation of the CRC 
value.

Parity is required to achieve the most reliable communications. If parity is enabled, 
both the Encompass 4H Reader and the host must issue a message if any received 
character has a parity error. However, the message must not be transmitted before 
receipt of the eom character. In this case, the Encompass 4H Reader will issue an