Software Handshaking - Motorola Symbol DS6878 Product Reference Manual

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 digital scanner expects either an ACK or
NAK response from the host. When a NAK is received, the digital 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
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: When this option is selected, 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.
RS-232 Interface 7 - 13