Aart's Blog

At the lowest level, the 6502 executes numerical machine code. For example, the following bytes in hexadecimal format constitute a simple program that displays a single 8 on the LED display of the Micro-KIM.   a9 ff 8d 40 17 a9 09 8d 42 17 4c 0a 02 Let's enter this program into the memory of the Micro-KIM. Power on the kit with jumper JP2 off and press the RS key. Then enter 0200 to set the address and press DA to go into data mode. Next, enter the numbers above pressing the + key after each number pair (so, enter A9 + FF + etc.). Before running, I strongly recommend checking the values. Use AD to go back into address mode. Press 0200 again and use + repeatedly to check all entered values. Once satisfied, press 0200 and GO. If all goes well, you will see a very bright 8 as first digit on the LED display (in later tutorials I will explain why). Displaying a single digit on the Micro-KIM Obviously constructing and entering programs this way is tedious and error-prone.

Perhaps reminiscing the past is a sign of getting older, but I cannot help but look back fondly at the times I learned programming machine code on the Commodore 64 in the eighties. Therefore, it is probably no surprise I still occasionally enjoy programming 6502 on the Micro-KIM, which is a modern replica of the seventies KIM1 microcomputer, made available by the well-known retro computer kits provider  Briel Computers . In fact, I am having so much fun with this board, I decided to write a series of tutorials on operating and programming the Micro-KIM. In this series, I assume you have already some experience with the Micro-KIM and 6502 machine code, and have read the basic documentation that is shipped with the kit. Other than that, I hope to give additional information on various topics, such as developing assembly programs, programming the display, using the RS232 port or keypad, setting up timer-based interrupts, using a cross-assembler to generate programs in paper tape fo

A rainy weekend was a perfect excuse to play with my micro-KIM, which had been collecting dust in a drawer for too long. I had fun using my own cross-assembler to develop and generate programs in paper tape format, and upload these to the micro-KIM via the PuTTY client. I figured out how to use the 6532 RIOT to set up a timer-based interrupt service, which is an important step in separating actual computation from display and keypad handling. The following clip shows the difference between incrementing a three-byte memory counter at roughly 1000 times per second (timer delayed) and 100,000 times per second (full speed with about 10 cycles per iteration at 1MHz). Perhaps a nice illustration of how fast even those early computers were.

Not everyone was happy with the "swipe-up" to open the options menus (for devices that lack a menu button, or that broke the legacy options menu altogether), so I decided to simply implement an on-screen button instead. I also improved the graphics in the on-screen buttons for navigation, something that as long overdue. The result is shown below. The right-most button with the horizontal lines opens the new-style options menu. As before, the other buttons are used for navigating the game, see the manual for details. On devices that still support a physical or virtual menu button (vertical dots in the screen-shot below), that button opens the legacy options menu. Expect a similar update for Reversi and Checkers for Android soon too.

A while back I got an email from Isaiah James D. Puzon, a computer engineering student at the Philippines FEU Institute of Technology, with a minor request for a new feature in Chess for Android that would help with his thesis project: a chess-playing robotic arm. It was very rewarding to receive pictures from his exciting working prototype a few months later. You did a great job building this robot arm, Isaiah. Congrats with your graduation and good luck with your further career!