The design and implementation of a programmable auxiliary keyboard for a microcomputer system

An auxiliary keyboard with 64 special function keys was designed, built and interfaced to a microcomputer system. In this case, the auxiliary keyboard was designed for an Apple //e microcomputer system.

The auxiliary keyboard, as designed, is separate from the Apple system keyboard and includes seventeen keyswitches. Each of sixteen keyswitches can be programmed with four separate key sequence programs. Selection of one of the four programs is done by the seventeenth keyswitch and indicated by LEDs on the auxiliary keyboard. Each key sequence program can contain up to 32 character codes which are sent to the computer when a key is pressed. All 128 ASCII character codes can be programmed into the auxiliary keyboard except the null character. The key sequence programs are stored in a 2K EEPROM which will retain the programs after the system power is turned off.

Interfacing to the Apple //e required that the standard Apple firmware input routines be modified. Additionally, programs were written to output characters to the screen, convert a binary format number to a binary-coded-decimal format number, take single character input from the Apple keyboard, and transfer data or programs from the Apple's RAM to an EEPROM. Both the 40-column mode and 80-column mode of the Apple //e were implemented in the auxiliary keyboard system software. Each routine was written in the 6502 Assembly language.

Hardware includes a keyboard interface card that plugs into the Apple's expansion slot number 5, a 2764 EPROM that replaces a ROM on the Apple motherboard, and an external keyboard. All previous functions and memory in the Apple //e were retained.