This project involves building a home computer centered on the 6802 Microprocessor. It features a hexadecimal keyboard with seven-segments displays for editing bytes in RAM.
This project was inspired by reading Ron Bishop's book:
An EEPROM 2864 is used to store the program responsible for managing key presses and display. This program is designed for this micro board, and the comments within the code provide details about the memory map, address mapping, and various sections of the program.
The program starts by defining the memory map, specifying the addresses for SRAM, PIA (Peripheral Interface Adapter) for 7-segment display, PIA for the keyboard, ASCIA (Asynchronous Serial Communication Interface Adapter), and EEPROM.
Configuration of PIAs for seven-segment display and keyboard is defined with specific address assignments. PIA configuration includes setting control registers, direction of input/output pins, and other parameters.
The program defines a data section with variables stored in RAM, including stack pointer, buffers for hex values and segment values of the display, and various other variables.
The program initializes the stack pointer, configures the PIAs, and sets up interrupt vectors. The reset vector points to the RSTVECT section.
The main program starts with the RSTVECT section, which initializes various components and displays the version information. The program enters a loop (NEWADD to NEXTKEY), waiting for keyboard input, processing key presses, and performing actions based on the pressed keys.
The program includes various subroutines for tasks such as displaying messages, beeping, handling interrupts, and processing keyboard input. Subroutines are used for specific tasks like displaying messages, handling keyboard input, converting hex to 7-segment display codes, and more.
The program has an interrupt vector (IRQVECT) that handles interrupts, specifically from the ACIA (Asynchronous Communication Interface Adapter). The interrupt service routine (IRQACIA) processes received characters and retransmits them.
There's an ASCIAINI section that initializes the Asynchronous Serial Communication Interface Adapter (ACIA) for serial communication.
The program includes functions for sending characters (SENDCHAR), printing strings (PRINTSTR, PRNTSTR2), and displaying messages on the 7-segment display.
Hexadecimal values are converted to 7-segment display codes using lookup tables (CODTAB). The CONVERTI subroutine performs this conversion.
There are subroutines for generating delays (DELAYA) and beeping sounds (BEEP, ALERTE).
In the early stages, I utilized a custom EPROM programmer specifically designed for the 2764, the original choice for this project. This programmer relied on dip switches and LEDs for manually inputting opcodes, with each code entered by pressing a button. Unfortunately, this manual process proved to be error-prone. There were instances where badly programmed locations were transformed into NOPs (No Operations), and program addresses had to be adjusted during the programming phase. The image below depicts the original programmer used for this purpose.
