The motherboard includes some simple input and output functions.

Output

The following are the output port addresses and their functions.

Hexadecimal	Decimal	Function
0x08	8	Status LED (low = on)
0x20	32	Serial port, request to sent (RTS)
0x28	40	Serial port, transmit data (TXD)
0x30	48	RAM bottom 64k selected (active low)
0x38	56	ROM selected (active low)

In each of the above cases, bit zero of the data byte determines the state of the output. If the onboard serial port is not in use, the serial port outputs can be used as simple digital output lines. These may be used for such purposes as turning LEDs on or off.

Input

A single input port is provided to read the serial data.

Hexadecimal	Decimal	Function
0x28	40	Serial port, receive data (RXD)

Bit 7 of the input port is the serial receive signal. This is a very crude input port and it is not recommended it be used for anything other than the serial receive input.

Decoding

The output port addresses are not tightly decoded. The full ranges of the output port addresses, expressed in binary and hexadecimal, are listed below.

Bits: 7654 3210	Hexadecimal	Function
0000 10XX	0x08 to 0x0B	Status LED (low = on)
0010 00XX	0x20 to 0x23	Serial port, request to send (RTS)
0010 10XX	0x28 to 0x2B	Serial port, transmit data (TXD)
0011 00XX	0x30 to 0x33	RAM bottom 64k selected (active low)
0011 10XX	0x38 to 0x3B	ROM selected (active low)

If the onboard serial port is not being used for serial output or simple digital output, the addresses 0x20 to 0x23 and 0x28 to 0x2B can be used by other devices on the RC2014 bus.

Software in ROM