Electronic – What type of processor in usual 8-digits pocket calculator

Architecturecalculator

There are a lot of +,-,*,/,CE,MC,M+,M-,MR buttons 8-digits calculators on market with keyboard layout like:

+----+----+----+----+
| ON | MRC| M+ | M- |
+----+----+----+----+
|  7 |  8 |  9 |  ÷ |
+----+----+----+----+
|  4 |  5 |  6 |  × |
+----+----+----+----+
|  1 |  2 |  3 |  - |
+----+----+----+----+
|  0 |  . |  = |  + |
+----+----+----+----+

Some of them have % and √ (sqrt) functions.

I wander what type of processor is under black epoxy lump? What is clock speed, registers bit width?

There are a lot of information about ancient '60, '70, '80 calculator architecture, advanced TI calculators and DIY projects but I can't find any mentioning of modern pocket calculator.

Best Answer

There are surely a lot of different ICs around for that application.

One I found was EMPCD081A, which has all the features you mention, as you can see in the datasheet, it runs with a 200kHz clock during operation (while calculating I assume) and 18kHz during wait operation. It can't shut down completely as it has to refresh the LCD and register a key press on the matrix. Running this slowly allows it to operate from a solar cell under very dim lights. It just takes 20µA maximum during operation.

My quick search has not revealed anything more specific on the internals of the chip (bit width of the registers).

Doing some further digging, there are some sources which suggest that they internally work with a 4-bit logic:

TC83220-0009: has a 4-bit oriented RAM (runs at 4MHz, but it can drive a printer, so it's a bit different)
MM57109: This is a really old design, but in this file a block diagram is depicted showing a 4-bit bus.

Related Solutions

Electronic – Identify processor type from raw binary code

Try running it through GNU file. If it's got any standard header, it'll pick it up.

Eg.

jrt@lin:~/src$ file foo
foo: ELF 32-bit LSB executable, Atmel AVR 8-bit, version 1 (SYSV), statically linked, not stripped

Electronic – What exactly is happening when a graphing calculator LCD malfunctions when batteries are weak or overloaded

All ICs (Integrated circuits or "chips") have a working voltage range outside which their behaviour is undefined. This means the manufacturers of the chips don't specify what will happen, just that it (probably) won't work as it should.

So the microcontroller in your Nspire may have a operating range of say 4V - 5.5V and outside this it might do just about anything. Typical stuff would be resetting, running code it's not meant to, etc.

This goes for all the other chips in there, including the LCD controller chip (the chip that drives the display) so odd behaviour is to be expected.
As long as the voltage is lower than it should be, damage will be very unlikely, it just won't work properly.

EDIT - some speculation:

My guess at what is actually happening is RAM that holds the pixel information for the LCD is not being read correctly at the lower supply voltages. Either that or the pixel matrix drivers are not transferring the data correctly.
It's hard to say without more info on the display type (e.g. TN, STN, TFT, OLED) as the method of driving them is a bit different. Also seeing the "fast moving lines" would help - for example if they are horizontal then that might fit with the scanning row by row from top to bottom that is usually the way the pixels are driven in LCDs.

Of course it's also possible the LCD read port is not reading correctly, the microcontroller is acting up, etc, etc. Normally it should have a low voltage sense and brownout active, but if it's in diagnostic mode these features are probably turned off.

All the effects described will be mainly due to the transistors no longer acting enough like switches as vicatcu discusses in his answer.

EDIT 2 - more info provided

Thanks for updating with more info. However, there's not much more that can be added which isn't vague speculation. To find the exact cause of things you would need to check things like: The display and microcontroller datasheets, microcontroller source code, scope the uC -> LCD connections, possibly even scope the LCD controller chip. Even then you may not be guaranteed to find the exact (original) cause as it may be on an unreachable part of the silicon (so all you see is secondary effects) for example an internal RC oscillator changing frequency so timing is not met on the chip, etc.

Best Answer

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Electronic – Identify processor type from raw binary code

Electronic – What exactly is happening when a graphing calculator LCD malfunctions when batteries are weak or overloaded

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