SC114, v1.0, User Guide, Port Addresses

The motherboard includes some simple input and output functions.


The following are the output port addresses and their functions.

0x088Status LED (low = on)
32Serial port, request to sent (RTS)
0x2840Serial port, transmit data (TXD)
0x3048RAM bottom 64k selected (active low)
0x3856ROM 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.


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

0x2840Serial 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.


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 3210HexadecimalFunction
0000 10XX0x08 to 0x0BStatus LED (low = on)
0010 00XX0x20 to 0x23Serial port, request to send (RTS)
0010 10XX0x28 to 0x2BSerial port, transmit data (TXD)
0011 00XX0x30 to 0x33RAM bottom 64k selected (active low)
0011 10XX0x38 to 0x3BROM 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

Homebrew 8-bit retro computing