Various Old Boards

These are some stuff I built, some from scratch and some from kits. I’m surprised some of the really old ones from high school survived (that would be about 30 years ago).

Poor Man’s EEPROM programmer

poor man's eeprom programmer

This was built during high school in Istanbul. I wanted to build a z80 based board and I didn’t have a way to program the eeprom IC. No computer to assemble either. So I hand-assembled monitor code from a book I found. I remember programming a test code and then leaving the eeprom chip outside under the sun to be erased. Of course, while programming the eeprom chip, I made mistakes. Luckily, two things saved me: programming EEPROM IC meant I can turn any bit from 1 to 0 (one way direction) and the NOP opcode for Z80 was 0x00. so when I made a mistake I turned that byte to NOP (0x00). But this meant some of the jump addresses already programmed get messed up due to shift, so I had to sprinkle additional jump instructions in the middle of upcoming subroutines, lol :) Good olds days.

On a side note, I am proud of myself for documentation :) The eeprom required 12V to program it, the top blue button was to switch supply between 5V and 12V. The yellow and red buttons were controlling a monostable circuit to (74LS123) to toggle the WE signal. The address and data busses were set manually via dipswitches. After I programmed the eeprom, I had to go back and verify all bytes were written correctly. the LED’s of course showed the data bus during write or read. I might have hand-programmed at least 2 Kbytes of memory :)

Cheap Man’s EEPROM programmer

simon6809 eeprom programmer

When I built simon6809, I planned on using it as a eeprom programmer too. I built a socket on top of the eeprom IC (had to sacrifice that guy) and put a wire between a testpoint on the board and the CE# of the top IC. If you plan on doing something similar, please note that once you write a byte to a memory location, you need to wait for the IC to complete writing. So you need to read back that location and wait until it reads back same. Of course, you need to unlock the EEPROM before you can write to it. All explained in the datasheets :)

6502 Single Board Computer w/ FTDI

6502 SBC FTDI

Probably early 2000’s. This might be my first attempt at getting FTDI UART board to work with 8-bit micros. it was always hassle to add a UART IC (6851, etc.) and MAX232 serial converter IC. I used FT245RL at work and had an idea to connect it the 6502 as a memory mapped device. Added benefit was the 5V supply from the USB port. After I built Simon6809 with this idea.

“Breaded” 68HC11 Board Computer

6502 SBC FTDI

This is from my university days. When I took the microprocessors class, our professor loved Motorola and so we used 68HC11. We used development boards at school, but I wanted to build my own. If I remember right, 68HC11 could start in a bootloader and download the initial code from the serial port.

Other Kits I built:

Apple One Kit

Apple One replicate with my EEPROM programmer mod :) From http://www.brielcomputers.com/wordpress/

COSMAC ELF Membership Card

Membership Card using RCA 1802 micro. From http://www.sunrise-ev.com/membershipcard.htm