Casio Pocket Calculator CPU Question

[DenverGuy]

This is a little nerdy, but I have always wondered what kind of CPUs basic calculators use. There is no way to identify them, as they now just look like a black blob. I use the calculator in the photo a lot and it's pretty good.
I was wondering if the processor really IS a CPU and if it has some of the basics of a computer CPU with an ALU, control unit, etc.
And is there a way to find out more about the cheap units used in basic calculators? I am always interested in what's going on under the hood.
Thanks.

[David Hayden]

The pages on this site for individual calculators all have links labelled "Technology" that take you to a page describing the hardware. Lots of details are known - enough to create high fidelity emulators of all(?) older HP models.

HP used it's own processor which evolved over time. The biggest difference from a general-purpose CPU is that the HP processors generally had 56-bit registers that could store a floating pointer number with mantissa and exponent BCD-encoded. Hardware instructions could do BCD arithmetic.

The address space is generally small, growing from 8 bits in the classics to 20 bits in Saturn CPU (the pioneers and the 48/49 series). Each address accesses a 10-bit value in the classics and in the NUT (41C) also. In the Saturn processor, each address accesses a 4-bit nybble.

Another thing I haven't seen in general purpose CPUs: the CPU registers could be accessed by "fields" - predefined groups of bits within the register. This let you read/write the parts of a number (sign, mantissa, exponent, exponent's sign), or individual nybbles within the number.

Starting in the 49(?), the Saturn CPU is emulated by an ARM processor (a general purpose processor that's very common in small devices). The 39gii and Prime use the ARM processor directly rather than via an emulated Saturn.

I'm sure that some of what I've written is wrong and that others will correct me.

[Mjim]

Not sure if you would find this interesting, but a tear down of the Casio fx-260 Solar 2 as well as looking at the chip under the blob was done here:
https://www.youtube.com/watch?v=HrsT1v34TH8

I found this reverse engineering integrated circuits video by Ken Shirriff video to be fairly educational (He also has a rather detailed blog as well: http://www.righto.com/):
https://youtu.be/aHx-XUA6f9g?t=78

[jklsadf]

Usually various mask-programmed, extremely low-cost microcontrollers:

http://www.kinpo.com.tw/English/product_consumer_1.html

[DenverGuy]

(01-09-2020 12:13 AM)Mjim Wrote:  Not sure if you would find this interesting, but a tear down of the Casio fx-260 Solar 2 as well as looking at the chip under the blob was done here:
https://www.youtube.com/watch?v=HrsT1v34TH8

I found this reverse engineering integrated circuits video by Ken Shirriff video to be fairly educational (He also has a rather detailed blog as well: http://www.righto.com/):
https://youtu.be/aHx-XUA6f9g?t=78

That's great! Thanks!

[Steve Simpkin]

It should be noted that the first calculator-on-a-chip, the Mostek MK6010, used for a four-function calculator was purely logic-based and did not have any embedded software/firmware on it. This was quickly followed by the Texas Instruments TMS1802 single chip calculator which was a small embedded processor (CPU) with RAM and software to implement a four function calculator all on one IC.

The story behind the race to develop the single chip calculator is fascinating reading.
http://www.vintagecalculators.com/html/t...-chip.html

TI went on to develop more complex custom embedded processors for their increasingly complex calculators. When they developed their first graphing calculator, the TI-81, they switched to a Z80 CPU which was used in a number of microcomputers including the TRS-80, Sinclair and many CP/M computers.
http://www.datamath.org/Graphing/TI-81.htm

When TI developed the TI-92 CAS calculator, they choose the Motorola 68000 CPU which was used in the original Macintosh computers.
http://www.datamath.org/Graphing/TI-92.htm

It is very fair to say that the race to develop large scale integrated circuits for the booming calculator market led directly to the development of the various microprocessors used in
microcomputers.
http://www.vintagecalculators.com/html/b..._4004.html