Software Handshaking - Motorola LI4278 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 linear imager scanner expects either
an ACK or NAK response from the host. When a NAK is received, the linear imager 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 linear imager scanner issues an error indication and discards the data.
The linear imager scanner waits up to the programmable Host Serial Response Time-out to receive an
ACK or NAK. If the linear imager 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 linear imager 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 linear
imager 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 linear imager scanner transmission off until the linear imager
scanner receives an XON character. There are two situations for XON/XOFF:
• XOFF is received before the linear imager scanner has data to send. When the linear imager 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 linear imager 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 linear imager scanner receives an XON character, it sends the rest of the data message.
The linear imager scanner waits up to 30 seconds for the XON.
RS-232 INTERFACE 7 - 13