Printronix T6000 Administrator's Manual page 178

You can select one of the following serial interface protocols to meet the host
interface requirements,
Series1 1 Char
Series1 2 Char
ENQ / ACK
DTR
178
Host IO > Serial > Data Protocol
The printer controls the flow of communication from the
host by turning the transmission on and off using
response characters sent to the host. If the number of
valid bytes in the buffer reaches 75 percent of the
buffer size, the ONLINE or OFFLINE and buffer full
response character is sent. If the buffer is completely
full, an ONLINE or OFFLINE buffer full response is
sent every time a character is sent from the host.
Whenever the printer state changes to ONLINE or
OFFLINE, the appropriate response character is sent.
If the idle response option is enabled, the printer will
send a response character every two seconds while
the number of valid bytes in the buffer is less than 75
percent of the buffer size. If a poll character is received
(configurable from the Poll Character xx Hex option on
the front panel from hex 0 through FF), the printer will
send a response character n milliseconds later
(configurable from the Poll Character xx MS on the
front panel from 0 through 30). This n milliseconds is
called the poll delay. The poll character will be
removed from the input data stream and will not be
processed. This may cause problems with the
transmission of binary data (e.g., control codes, bit
image, etc.). If a poll delay is started due to the receipt
of a poll character and another poll character is
received, the second poll character has no effect and is
removed from the input data stream. If a transition
(from buffer full to empty or ONLINE to OFFLINE)
occurs during a poll delay, the new printer state will be
sent at the end of the poll delay. See Table 3.
This protocol behaves exactly the same as the Series 1
Char except there is a two-character response to the
host. The response characters are described in Table 3.
The host controls the flow of communication to the
printer by sending a block of data and ending the block
with an Enquiry (ENQ) character. When the printer
receives the ENQ Character, it acknowledges the
ENQ, thereby acknowledging it has received the entire
block of data. Status will also be sent before the ACK.
The status is as shown in Table 4.
The printer controls the data flow by sending this
hardware signal to the host. If there is enough room in
the printer buffer, the printer will send a high signal; if
the buffer is full, the printer will send a low signal. DTR
tells the host if it is safe to send more data. (If the host
sends data during an unsafe condition, data will be
lost.) DTR is not available when RS-422 is selected