Serial Mode Plug And Play; Using Dsr; Serial Device Identification - TransAct Ithaca 90PLUS Series Programmer's Manual

Programmer's Guide
8.3.6

Serial Mode Plug and Play

Microsoft has defined a Plug and Play (PnP) protocol to identify devices on serial links. This enumeration
process is designed to find and automatically configure a device driver for the printer. It is done by toggling
the control lines in a specific sequence that is recognized by the printer. The peripheral then responds such
that Windows can identify the device.
To allow the printer to look for and respond to this sequence, PnP must be enabled. When enabled in serial
mode, the flow control is forced to RTS with DTR static. The off-line flag can also be set.
8.3.6.1
Windows uses the host's DSR line (the printer's DTR line) on the serial port to determine whether a
device is attached to the port. When Windows is booted, the system sets the host's DTR and RTS to
zero and waits approximately 200 milliseconds. It then sets DTR to one and waits another 200
milliseconds. At the end of this time, the system checks to see whether the DSR line is high, indicating
that a serial device is attached to the serial port. The system responds by setting RTS high and waits to
receive the device identification string.
In some devices, such as a serial mouse, the DSR line can be held high by tying it directly to the DTR
line. When the mouse is connected to the serial port on the personal computer, the power supplied
through the DTR line also raises DSR high.
For Plug and Play compatibility, DSR must stay high as long as the device is attached to the serial port.
This is why RTS flow control is used at the printer.
8.3.6.2
The serial device must report its identification to the system using an identification string at 1200 baud.
The identification string consists of 18 fields that identify the device, device class, and other
compatible devices. Only five of the fields are required by all serial devices; all others are optional.
The identification string used by the Series 90PLUS Printer follows:
028H
0,1
IPR0210
\PRINTER
\S90 PcOS
xxH
029H
Note: The model field may be altered to generate PnP ID's other than "\S90 PcOS" by special order.
When the identification is complete, the printer returns to the baud rate specified in the configuration.
11/07/05
PcOS Series 90PLUS

Using DSR

Serial Device Identification

Start of ASCII response
PnP Rev
Unique ID (IPR plus revision level)
Printer
Model
Check-sum
End PnP
Rev Q
Communications
Serial Port
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