Expansion Ports

There are currently 3 hardware expansions built into the emulator. There are plans to allow for custom ones but that hasn’t been implemented yet.

Types

Keyboard

The keyboard expansion detects key presses from the keyboard. The keycode is sent using the lower 8 bits (0bXXXXXXXX). They are automatically converted by hardware from ASCII to the SDCII format before reaching the expansion port.

Mouse

The mouse expansion port holds multiple pieces of data:

binary:  R L XXXXXXX YYYYYYY

You should process the data before using it, by bit shifting and bitwise AND-ing the numbers. The following example uses C for simplicity, but can very easily be translated to Yabal, and with a bit more effort, Armstrong. The variable titled mouseVal is assumed to be the expansion port value of the mouse.

bool rightMousePressed = (mouseVal >> 15) & 1;  // Shift value from the left side to the right and get it by itself
bool leftMousePressed = (mouseVal >> 14) & 1;  // Shift value from the left side to the right and get it by itself

int mouseXPos = (mouseVal >> 7) & 0b1111111;  // Shift X coord value from the left side to the right and get it by itself
int mouseYPos = mouseVal & 0b1111111;  // Get y coord by itself

Sound Card

The sound card is a 4 channel audio output device. It has squarewave A, squarewave B, triangle wave, and noise. The binary data encoding looks like this:

binary:  FFFFF CCC

The frequency is a value between 0 and 32. The channel is a value 0 through 4.

To change the frequency of a channel, send a value to the expansion port like: 0b00001001, which would set the second channel (squarewave B) to play at a frequency of 1 (not in Hz, see conversion table). If a channel is not playing when you change it’s frequency, it will begin playing. To stop the playback of a channel, send a second value to the expansion port with a frequency of 0, like: 0b00000001 which would turn off the second channel.

Due to only 5 bits of precision, frequencies are approximated, and you can see the conversion table to compare values sent to the expansion port with their corresponding actual frequencies.

Conversion table