More Calculator Processors

Last year I wrote a post about a lot of different processors that could be used to make a calculator. Recently I decided to buy some of them from the CPU Shack Trade List and found some others that might also work. John, who sold me the chips, was really helpful and sent everything very quickly.


These are the processors from the last post that I got examples of:

CDP1806ACE
E87C196KDH20
N80960SA-16
N80C196KC16
NS32FX164V-25
TMS320C25FNL

The really exciting one is the NS32FX164. It seems like a really neat chip, and I was having trouble finding any of the NS32FX160 series chips to play with. There are a lot of variants built on this core, and this seems like one of the best ones to have. The instruction set is really interesting since there are so many options and extensions. This is definitely a CISC processor.

These are new chips not covered in the last post:

2650AN - This is an 8 bit microprocessor with more registers and instructions that a 6502. However, it has a strange 13-bit address system that makes it less useful than all the other processors that can address at least 16 bits. The one I got is the A version which is missing some of the added instructions of the B version. Top speed is apparently 1.25MHz.

INS8073/N - This is another 8 bit chip that that also has limited addressing potential. The main appeal of this processor is that it has a version of BASIC built into ROM. I don't think I would rely on that for the calculator's main language, but it might be neat to have it as an option to play with. Hopefully there is a way to boot from external memory and jump into BASIC later.

L3903-57 - This is part of an offshoot of the 6502 family that was used as part of modem chipsets. It has a lot of microntroller features like internal RAM and peripherals like timers. It runs at up to 20.5MHz, compared to the 8MHz of the 6502 derived microcontroller made by WDC and the 14MHz of a 65C02. It is not entirely compatible with the 65C02 since it handles indirect jump instructions differently and has additional instructions for threaded code. It might have more flexible timing constraints, which could be helpful even if it isn't running at top speed.

N8X305N - This is the weirdest processor in the list by far. It has a 16-bit wide instruction bus but no dedicated bus for data. External data access can only be conducted through two "ports." The really strange thing about this chip is that it only has eight instructions. The OR instruction, for example, has to be synthesized from AND and XOR. It seems like it would be a big challenge to write assembly for this.

SAB80199 - This is a neat 16-bit chip made by Siemens. Unfortunately, I can't find a datasheet for it, so I'm not sure yet if it would work well for a calculator. I paid to access the datasheet database at eca.de, but the link they sent was broken. Hopefully they will respond to my messages soon.

As I wrote in my another post, I'll have to finish some of the projects I have open now before I start on something with one of these chips.

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.