DSP 104-plus, Reference Manual

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In RS-485 mode the DTR control output has no effect, and the CTS, DCD, DSR and
RI status inputs are undefined (they can be in either state, and software must not
assume any particular values of these signals).
No RS-485 termination resistors are provided on the TP400. These must be provided
externally if required.
When operating as an RS-485 port the COM2 RS-232 signals on connector J4 are
re-assigned. Appendix E provides information on RS-485 pin assignments.
3.4.3 Disabling Serial Ports
The COM1, COM2, COM3 and COM4 serial ports can be individually disabled by the
BIOS Setup program (use the Advanced / I/O Device Configuration menu). See
section 6.2 for details of the Setup program.
3.4.4 Extended Modes
The serial ports within the PC97317 Super I/O chip may be programmed to operate in
"extended mode". This allows for operation at up to 1.5M baud, using DMA to transfer
data and provides more sophisticated interrupt handling.
The BIOS does not support this extended mode, but users who need these features
may reprogram the PC97317 registers to suit their needs.
3.4.5 Infra-Red Operation Modes
(At the time of writing the TP400 BIOS does not support the IrDA mode of the Super
I/O chip. The rest of this section describes how the IrDA would operate if and when
the BIOS implements IrDA. Contact DSP Design if you have an IrDA application.)
The COM2 serial port can also be configured to operate in one of three infrared
modes, transmitting and receiving data as infrared light pulses. The three modes are
IrDA, Sharp-IR and Consumer-IR. At present the BIOS only configures the COM2
UART for some of the modes, but users who need the other modes may reprogram
the PC97317 registers to suit their needs.
The IrDA standard defines a number of protocols. The TP400 supports the SIR
format, with speeds of up to 115k baud. The IrDA transmit and receive data signals
(IRTX and IRRX) are available on the 50-way I/O connector J4 pins 2 and 1
respectively, from where they can be connected to an IrDA infra-red transceiver
module. The TCDEVPLUS (but not the TCDEV) incorporates a suitable IrDA
transceiver.
To configure the COM2 serial port as an IrDA port you must use the Advanced / I/O
Device Configuration menu within the BIOS Setup program (see section 6.2 for
details of the Setup program). This sets a bit in an internal Super I/O configuration
register, so that COM2 data is routed through the IRTX and IRRX pins on the Super
I/O chip, rather than the pins that connect to the RS-232 transceiver chip. The COM2
handshake lines, however are still routed through the RS-232 transceiver chip and
behave as in normal RS-232 operation.