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LT 1804 Product Reference Guide: Programming the LT 1804
Software Handshaking
The scanner also provides two software handshaking options, ENQ and ACK/
NAK, selected by parameter menus.
These software handshaking options operate in addition to, and are
subordinate to, the hardware handshaking. They can be used separately, in
conjunction with each other, or not at all. They operate in the following
manner:
When the ENQ is enabled, the scanner waits for an ENQ, Enquire,
•
character from the host before it transmits data. The host must respond
within the programmable response timeout period or the scanning unit
beeps 4 times, indicating transmission error and loss of the last scanned
data.
When the ACK/NAK is enabled, after the scanning unit has transmitted
•
data, it looks for one of the following responses:
<ACK> acknowledging a valid accepted transmission, or
<NAK> indicating a problem with the transmission.
The scanner then retransmits the data. After three unsuccessful
transmission attempts, the unit aborts any further communication
attempts on the current message. It indicates this by sounding 4 long
(1 second) beeps.
See
Handshaking Sequence on page
4-23.
4-22
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