[chbot] Help track down a processor - the double chox fish challenge

Stephen Irons stephen at irons.nz
Thu Jun 24 07:47:58 BST 2021

Padauk PFS173-S20 is a SOIC-20 and has power on 6 and ground on 15 -- 
the opposite of yours -- and pins 12 and 13 can be an analog input to a 
comparator with an adjustable reference.

Perhaps some of their other series have a different pinout. See 

In case you are attracted to 'the 3c microcontroller'
C-like language, but really just assembler with some C syntax for loops 
and conditionals, etc.No stand-alone command-line compiler, so cannot 
automate building, etc.Home-grown IDE with all of the disadvantages of 
a home-grown IDE.Windows only tools.Inaccurate in-circuit emulator. At 
least they do provide one, but it has significant differences from the 
real parts. Also, it only works with the low-grade debugger in the 
home-grown IDE.Buggy datasheets. They do have errata, but you have to 
look for them. I see that they now have one dated 2020-06, so perhaps 
that problem has gone away.In-circuit programming needs dedicated pins 
or careful thought as it needs high voltages.
It has an analog comparator, timers and PWM generators, but no other 
peripherals (UART, SPI, I2C, etc). I implemented a bit-banged I2C slave 
on a PFS173-S8 (SOIC-8).

I would not use them again, unless a cost-benefit analysis showed that 
it would be an advantage. You would need significant quantities to 
offset the cost of learning the ins and outs of new tools, new 
archtecture, etc. Our client was hooked by the '3c' bit, and bought all 
of the (really cheap) tools, but failed to appreciate how expensive 3 
weeks of debugging might be, to find and fix a race condition that 
happens once per hour on the torture test jig, and to radically modify 
the software when one of the external time-constants turned out to be 
too long for the 8-bit timer, and to find out that there was no 
reliable way to increment on counter overflow and not miss I2C events, 
and so on.

I would use an STM32 or similar for a dollar or two, and get the 
hardware to do stuff that hardware is good at.

Stephen Irons

On Wed, Jun 23, 2021 at 13:10, Mark Atherton <markaren1 at xtra.co.nz> 
> For those with way too much spare time on their hands.
> I have a CPU based Chinese product which requires some firmware 
> updates (probably a complete rewrite).
> Finding a pin-compatible part with a low cost tool-chain is also OK.
> This is not a commercial exercise.
> CPU has 20 pins, SOIC package
> Pin 5 - I2C
> Pin 6 - GND
> Pin 7 - I2C
> PIN 12 - ADC
> PIN 13 - ADC
> PIN 15 - 3V3
> Pretty much all of the other pins are GPIO.
> Almost like ATtiny87, except I2C required either side of the GND pin.
> I started by using Digikey as the sifting and sorting agent, just 
> wondering if their is a better way.
> -mark
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