Rice Lake Motorola DS457 Laser Scanner - Manual (Page 159)

Serial Interface 9 - 13
Software Handshaking
This parameter offers control of data transmission in addition to, or instead of, the control hardware
handshaking offers. There are five options.
If software handshaking and hardware handshaking are both enabled, Hardware Handshaking takes
precedence.
• None
: Data transmits immediately. No response is expected from host.
• ACK/NAK
: After transmitting data, the imager expects either an ACK or NAK response from the host.
When the imager receives a NAK, it 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 imager issues an error
indication and discards the data.
The imager waits up to the programmable Host Serial Response Time-out to receive an ACK or NAK. If
the imager does not receive 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 imager waits for an ENQ character from the host before transmitting data. If the imager does
not receive an ENQ within the Host Serial Response Time-out, it 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 imager transmission off until the imager receives an XON
character. There are two situations for XON/XOFF:
•
The imager receives an XOFF before it has data to send. When the imager has data to send, it waits
up to the Host Serial Response Time-out for an XON character before transmission. If it does not
receive an XON within this time, the imager issues an error indication and discards the data.
•
The imager receives an XOFF during a transmission. Data transmission then stops after sending the
current byte. When the imager receives an XON character, it sends the rest of the data message. The
imager waits indefinitely for the XON.