Serial Port Inquire - TransAct POSjet 1500 Programmer's Manual

Port Protocols and
Connection Specifics

Serial Port Inquire

The serial port inquire is more straightforward than parallel mode. The serial acknowledged (ACK) or not
acknowledged (NAK) responses follow a uniform format, the ACK or NAK is always followed by the command ID
that requested it. This makes the design of the host application easier because the response can be identified and
always follows the same format.
The host
inquire to the printer
asking for the form
sensor status.
The host receives the
response and decodes it.
The host sends an [ENQ] <id> (form sensor status) request to the printer. The printer responds with an [ACK] <id>
indicating that the request was identified, status true.
Inquire commands affect the printer's performance. Communication is a high priority for the printer. Inquire
commands take processing time away from the print tasks. It is possible to ask for so much status that the printer
slows. In serial mode, it is important that the response to an inquiry is received by the host before another command
is issued. When an inquiry is received by the printer, it is buffered in a high-speed processing queue. When the
printer has time, it empties the queue and processes the inquiries. The printer responds to the command as soon as
the second byte of the command is taken from the high-speed buffer. If the host is looking for a form to be inserted,
it should not send status requests as fast as it can. The host will receive a response to all of them. If the host did not
wait for a response to each, there would be unnecessary responses.
In IEEE 1284 mode, inquire responses are placed in an IEEE 1284 transmit queue. When the IEEE 1284 reverse
channel is open, the responses are returned to the host. It is important that after each request the reverse channel be
opened. Inquire responses remain in the queue until read. If the [ENQ] <9> command is sent to the printer, the
IEEE 1284 buffer will be cleared, and only the response to the [ENQ] <9> will remain.
Page 264
®
POSjet
sends an
Flow Chart 3 Inquire Flow
Rev M
1500
The printer receives the
request and preprocesses
it.
The printer responds
with an [ACK] <id> or
[NAK] <id> indicating
the form sensor status.
Programmer' s Guide
Nov-07