Software Handshaking - Symbol LS 1220 Product Reference Manual

Software Handshaking

This parameter controls the data transmission process. It may be used in conjunction with
Hardware Handshaking. However, Hardware Handshaking takes precedence. That is, it
takes place before, and ends after Software Handshaking. All references to beepers
presuppose a beeper is present.
The scanner provides four Software Handshaking options; NONE, ENQ, ACK/NAK, and
ACK/NAK with ENQ. Refer to the Software Handshaking diagram, Figure 8-2.
1. None
No handshaking is selected and data is transmitted immediately.
2. ACK/NAK Only
The ACK/NAK option checks the success or failure of a transmission. The scanner
expects one of the following host responses after a data transmission:
<ACK> - Acknowledges a valid and successful transmission.
<NAK> - Indicates a problem with the transmission.
Whenever a <NAK> is received, the scanner retransmits the same data and awaits an
ACK/NAK response. After three unsuccessful attempts to transmit the same data, the
scanner aborts any further communication attempts on that message. The beeper
indicates a transmission error by sounding 4 long beeps.
3. ENQ Only
With this option, the host must request data before the scanner sends it. This ensures
that data transmission occurs only when the host is ready to receive.
When this option is selected, the scanner waits for an Enquire character (ENQ) from
the host before it transmits data. With ENQ enabled, the scanner must receive an ENQ
from the host within 2 seconds after the last activity or the scanner sounds four long
beeps to indicate a transmission error; the unit is now ready to scan again.
4. ACK/NAK with ENQ
This combines both handshaking options.
Programming
8-15