Software Handshaking - Symbol LS4278 Product Reference Manual

7-14 LS4278 Product Reference Guide

Software Handshaking

This parameter offers control of the data transmission process in addition to, or instead of, that offered by hardware handshaking.
There are five options.
If Software Handshaking and Hardware Handshaking are both enabled, Hardware Handshaking takes precedence.
• None: When this option is selected, data is transmitted immediately. No response is expected from host.
• ACK/NAK: When this option is selected, after transmitting data, the scanner expects either an ACK or NAK response from
the host. When a NAK is received, the scanner transmits the same data again and waits for either an ACK or NAK. After
three unsuccessful attempts to send data when NAKs are received, the scanner issues an error indication and discards the
data.
The scanner waits up to the programmable Host Serial Response Time-out to receive an ACK or NAK. If the scanner does
not get a response in this time, it issues an error indication and discards the data. There are no retries when a time-out
occurs.
• ENQ: When this option is selected, the scanner waits for an ENQ character from the host before transmitting data. If an ENQ
is not received within the Host Serial Response Time-out, the scanner issues an error indication and discards the data. The
host must transmit an ENQ character at least every Host Serial Response Time-out to prevent transmission errors.
• ACK/NAK with ENQ: This combines the two previous options. For re-transmissions of data, due to a NAK from the host,
an additional ENQ is not required.
• XON/XOFF: An XOFF character turns the scanner transmission off until the scanner receives an XON character. There are
two situations for XON/XOFF:
• XOFF is received before the scanner has data to send. When the scanner has data to send, it waits up to Host Serial
Response Time-out for an XON character before transmission. If the XON is not received within this time, the scanner
issues an error indication and discards the data.
• XOFF is received during a transmission. Data transmission then stops after sending the current byte. When the scanner
receives an XON character, it sends the rest of the data message. The scanner waits up to 30 seconds for the XON.
*
None
ENQ
ACK/NAK