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.