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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 decoder expects either an ACK or NAK response from the host. When
the decoder 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 decoder issues an error indication and
discards the data.
The decoder waits up to the programmable Host Serial Response Time-out to receive an ACK or NAK. If the
decoder 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 decoder waits for an ENQ character from the host before transmitting data. If the decoder 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 decoder transmission off until the decoder receives an XON
character. There are two situations for XON/XOFF:
• The decoder receives an XOFF before it has data to send. When the decoder 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 decoder issues an error indication and discards the data.
• The decoder receives an XOFF during a transmission. Data transmission then stops after sending the
current byte. When the decoder receives an XON character, it sends the rest of the data message. The
decoder waits indefinitely for the XON.
Serial Interface 7 - 13
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