Calculator Processors

Most of the microcontrollers and processors I have looked into using have been for my calculator projects. That's one of the main reasons I did my microcontroller comparison a few years ago. Recently, I have gotten interested in other chips I could use for calculator projects, in addition to the 6502, 6800 family, and 8051 chips I was interested in before.

The main two criteria I have are an external memory bus and through-hole package. Right away, this eliminates most modern microcontrollers, since almost all of them with an external memory bus are SMD only. In theory, I could use a chip without an external bus if it had a few hundred KB of RAM for data and a few hundred more KB of RAM or flash for program space, but I haven't found that in a through-hole package. Another point is that I would like the ability to load programs from an SD card, which is impractical if I need to have the chip reflash itself every time I load a program. Through-hole parts are more convenient to solder, and I would like to do a few more projects with them before I try to start making surface mount boards.

Modern microcontrollers

• AVR - None of the ATmega series has an external bus. Some of the ATxmega series do, but they don't come in through-hole packages.
• PIC - For a through-hole part, the PIC32 series is very impressive at 50mhz with 64KB RAM and 256KB of flash, but even this is not enough for what I am planning. The chip requires a separate programmer, and the compiler offers limited optimizations unless you pay, which is absurd in 2018 compared to its competition. It does have something called PMP, which offers a sort of data bus, but it can only address 12 bits, since the DIP part only has 28 pins. 
• MSP430 - This chip worked well for my RPN Scientific Calculator, but it also lacks an external bus.
• Propeller - This is an interesting chip but like the others, it lacks an external bus and does not have enough flash or RAM. The one interesting possibility is doing several calculations in parallel, although I don't know how I would use that for a calculator.
• Zilog - They have some nice chips, including some processors with external buses, but I would like to use something different than what the TI-83 and similar models use.
• LPC1114 - I really like this chip, and I am using it in my Pocket Calculator, but it also lacks an external bus, and it seems that it is no longer manufactured.

6800 Family Tree

After about two years away from electronics, I have some time for my projects now that I am almost finished with my degree. Lately, I've been thinking about a lot of things and I want to start some new calculator projects and pick up where I left off on some other projects. One thing I have been thinking about is working on a simpler 6502 based calculator than I was working on before to get more experience working with the chip. I think the 6502 graphing calculator I was working on did not turn out very well because I rushed through everything too fast trying to get ready for Makevention in 2015.

Along those lines I recently got curious about other chips I could use to make a calculator. The last time I was curious about that I compared some of the microcontrollers I was interested in to see how fast they compute. One of my plans now is to do some other comparisons, which I think will be more useful. This time I want to compare processors like the 6502 as well, so I looked at other chips that would be fun to use. One group that I have been interested in for a while is the 6800 family like the 6809 and 6309. I could not find a family tree on the internet, so I started making one myself. When I was almost done, I found this tree in a document about the 6804: