Instead I used an old Arduino Mini Pro I had laying around, which IS 5V-based. Unfortunately the display does NOT like 3.3V and I really didn't want to use 8 level converters. The contrast voltage is 8-12V, so I bought a cheap variable DC-DC step up converter. I have more than 50 of them and have always wondered what to do with them. The 40x3 text LCD I had lying around was a salvage from old corporate desktop telephones. A BSS138-based level converter solved that. It works most of the time, but fails sometimes. Turns out most PS2-keyboards are happy to be driven by 3.3V but the one I have does not like it. The Arduino environment was REALLY nice to use, most things had decent libraries ready to use, I just had to tweak them a bit to use on the Teensy. Only problem: NOT 5V compatible which is problematic when using the text-display I had laying around, and ps2-keyboard interfacing.Īt this point I started connecting HW to the Teensy one at a time, to solve the HW & SW interfacing. Parallel access to pins in Arduino is something that is hard to do, which also weighed against this approach.Īfter some search and thought I bought a Teensy 4.0 which is a real beast! 600MHz of 32-bit cpu goodness with HW floating point, 1024kb RAM plus all the peripherals I would need. I started looking at adding an external parallel SRAM to fulfil my RAM requirements, but quickly abandoned the idea when I realised how many pins had to be soldered and also the fact that I might have to use an external register to get enough signals. Clearly not ideal, even if the bread-boarding of an SPI-RAM is VERY simple. This was when the memory was random-accessed, and going to sequential accessed memory increased the bandwidth to just less than 2MHz, but varied wildly depending on work done. Inspired by Shane Goughs TGL6502 I tried to get around this by using an SPI RAM-memory but the memory bandwidth meant a 6502 speed of only around 0.5MHz. The problem with the Blue Pill is limited RAM, only 20kb, and I wanted at least a 128kb bank switched 6502 system in the end. It took very little effort to get it working, and I immediately implemented ehBasic which is extremely nice to use as a debug- and test-environment of the emulated HW-components. The 6502-emulator I used was a slightly modified version of fake6502 by Mike Chambers. Generation 1 of the system ran on a cheap Blue Pill that can use the Arduino framework.
Soldering is fun for just a short while before it gets tedious :)Ī good compromise between HW, SW and mechanics I came up with involves emulating most of the system components in software on small microcontrollers. I certainly have the skills to do it, but I dislike the work involved.
We have indeed come a long way.When I decided I wanted to code on the 6502 again and realized I didn't have a physical retro platform I could use, I contemplated building a real HW 6502-system.
It is fun to think that the meager capabilities represented by an Arduino is able to simulate the silicon that was available back when I first started working with micro-controllers. I will provide some pictures as soon as I figure out what box contains that little treasure. I still have my 6502 system built back in the mid-1970's.
Cross-compilers and assemblers were built and utilized to program our new hardware. Bringing our loot home spawned a lot of effort to build and program working systems. At the time, Motorola was selling the 6800 microprocessor for a single unit price of $175 and ended up dropping the price to $69 in single unit quantities with further price reductions to follow.
The hardware and programming documentation manuals were another $10. I was at the time working for Hewlett Packard Advanced Products Division in Santa Clara, CA interestingly enough in the same group of teams that employed Steve Wozniak who later went on to found Apple Computer.Ī group of us went to the trade show in the fall of 1975 and were able to purchase the 6502 for $25. This was fun for me because my first experience with micro-controllers was when the MOS Technology 6502 was introduced at the Wescon trade show in San Francisco in 1975.