Serial Port Inquire; Figure 31 Inquire Flow - TransAct Ithaca 90PLUS Series Programmer's Manual

Communications
Serial Port
8.3.7

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 sends an
inquire to the printer
asking for the form
sensor status.
The host receives the
response and decodes
it.

Figure 31 Inquire flow

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, and the status is true.
Inquire commands affect the printer's performance. Printer communications are a high priority. Inquire
commands take processing time away from print tasks. It is possible to ask for so much status that the
printer slows down.
In serial mode, it is important that the response to an inquire command be received by the host before
another command is issued. When an inquire command 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 inquires. The
printer will respond 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 get 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, inquiry 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 will 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.
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PcOS Series 90PLUS
The printer receives the
request and
preprocesses it.
The printer responds
with an [ACK] <id> or
[NAK] <id> indicating
the form sensor status.
Rev Q
Programmer's Guide
11/07/05