Software Handshaking - Motorola DS6878 Reference Manual

8 - 12 DS6878 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: Data is transmitted immediately. No response is expected from host.
•
ACK/NAK: After transmitting data, the digital scanner expects either an ACK or NAK response from the
host. When the digital scanner receives a NAK, it re-transmits the data and waits for either an ACK or
NAK. After three unsuccessful attempts to send data after receiving NAKs, the digital scanner issues an
error indication and discards the data.
The digital scanner waits up to the programmable Host Serial Response Time-out to receive an ACK or
NAK. If the digital 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: The digital 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 digital 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 digital scanner transmission off until the digital scanner
receives an XON character. There are two situations for XON/XOFF:
• XOFF is received before the digital scanner has data to send. When the digital 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 digital 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 digital scanner receives an XON character, it sends the rest of the data message. The
digital scanner waits up to 30 seconds for the XON.