Software Handshaking - Motorola DS9208 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: Select this to transmit data immediately. The digital scanner expects no response from the host.
•
ACK/NAK: If you select this option, after transmitting data, the digital scanner expects either an ACK or
NAK response from the host. When it receives a NAK, the scanner transmits the same data again 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 Timeout 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 timeout occurs.
•
ENQ: If you select this option, the digital scanner waits for an ENQ character from the host before
transmitting data. If it does not receive an ENQ within the Host Serial Response Timeout, the digital
scanner issues an error indication and discards the data. The host must transmit an ENQ character at
least every Host Serial Response Timeout 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 scanner receives an
XON character. There are two situations for XON/XOFF:
• The digital scanner receives an XOFF before has data to send. When the scanner has data to send, it
waits up to Host Serial Response Timeout for an XON character before transmission. If it does not
receive the XON within this time, the digital scanner issues an error indication and discards the data.
• The digital scanner receives an XOFF 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 indefinitely for the XON.
RS-232 Interface 7 - 13