Intermec Transaction Manager 9560, Руководство пользователя

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9560 Transaction Manager User’s Manual
5-8
User-Defined and User-Defined Multi-Drop Protocols
You define all protocol parameters in User-Defined protocols. Thus, you can
duplicate any protocol to emulate a proprietary or irregular protocol on a host
computer.
Some protocols are very robust and secure, while others are not. A secure data
link protocol can recover from transmission line errors (parity and framing
errors) and uses affirmative and negative responses to verify communication
events. If the transmitting device receives a negative acknowledgment, the data
is retransmitted. The maximum retry count is three for all asynchronous
Intermec protocols.
Tips for Defining Secure Protocols
Use these tips for defining secure User-Defined protocols:
1. Define all protocol fields with ASCII control characters. See the Glossary for
definitions of unfamiliar acronyms and terms. Examples:
SOM = STX REQ = ENQ
AFF = ACK RES = EOT
NEG = NAK EOR1 = RS
EOM1 = ETX EOF = ETB
2. Use even or odd parity when transmitting data.
3. Enable the LRC (Longitudinal Redundancy Check character) to provide
added data security to all transmitted and received messages. When both
parity and LRC checks are enabled, horizontal and vertical error checking
are performed. If the SOM is enabled, it is not included in the LRC
calculation. The reader allows the LRC to be enabled in addition to
XON/XOFF flow control. The host device must also be able to receive the
XON or XOFF character as the LRC or receive the XON or XOFF characters
as data if preceded by the DLE.
4. If the host device cannot guarantee reception of data at all times, the host
should control the transmission of data from the reader. There are three
methods available. Use one of the methods or combine them:
a. Enable Solicitation. This prohibits the reader from sending any type of
data or response unless the host is ready for it.
b. Enable XON/XOFF flow control.
c. Use CTS (clear to send) hardware handshake. The reader checks CTS
before transmitting all characters with the exception of XON/XOFF
responses. If CTS is false, the reader either stops or does not start
transmitting data.
5. Always enable the SOM.