Printronix t8000 Administrator's Manual page 187

Host IO > Serial > Data Protocol
You can select one of the following serial interface protocols to meet the host
interface requirements,
The printer controls the flow of communication from the
host by turning the transmission on and off. In some
situations, such as when the buffer is full or the timing
of signals is too slow or too fast, the printer will tell the
host to stop transmission by sending an XOFF
character. An XOFF character is sent when the
number of empty bytes in the buffer is less than or
XON / XOFF
equal to 25 percent of the buffer size. If the host keeps
sending data after an XOFF is sent, the printer
firmware will continue to send an XOFF for every 16
characters received. When cleared, the printer will
resume receiving data (XON). The data does not have
any End of Text codes; XON / XOFF is a non- block
protocol
End of Text / Acknowledge. The host controls the flow
of communication to the printer by sending a block of
data and ending the block with an End of Text (ETX)
ETX / ACK
signal. When the printer receives the ETX signal, it will
acknowledge the ETX, thereby acknowledging it has
received the entire block of data.
ACK means acknowledge; the device acknowledges it
has accepted a transmission. NAK means negative
ACK / NAK
acknowledge; the device did not receive the
transmission
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