RS-232 Interface 8 - 13

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 handshak ing takes precedence.
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None: Select this to transmit data immediately. The device expects no response from the host.
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ACK/NAK: If you select this option, after transmitting data, the device expects either an A CK or NAK
response from the host. When it receives a NAK, the device transmits the same da ta again and waits for
either an ACK or NAK. After three unsuccessful attempts to send data after receiving NAKs, the device
issues an error indication and discards the data.
The device waits up to the programmable Host Serial Response Time-out to receive an ACK or NAK. If the
device does not get a response in this time, it issues an error indicati on and discards the data. There are no
retries when a time-out occurs.
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ENQ: If you select this option, the device waits for an ENQ character from the host be fore transmitting data.
If it does not receive an ENQ within the Host Serial Response Time-out, the device issues an error indication
and discards the data. The host must transmit an ENQ character at least every Hos t Serial Response
Time-out to prevent transmission errors.
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ACK/NAK with ENQ: This combines the two previous options. For re-transmissions of data, du e to a NAK
from the host, an additional ENQ is not required.
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XON/XOFF: An XOFF character turns the device transmission off until the device rec eives an XON
character. There are two situations for XON/XOFF:
•The device receives an XOFF before has data to send. When the device has data to sen d, it waits up to
Host Serial Response Time-out for an XON character before transmission. If it does not receive the XON
within this time, the device issues an error indication and discards the data.
•The device receives an XOFF during a transmission. Data transmission then stops after s ending the
current byte. When the device receives an XON character, it sends the rest of the data message. T he
device waits indefinitely for the XON.