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

[Mark Atherton]

Thanks, Stephen, Charles, Everyone.

Current plan is to just make a new board with a '328; more than enough 
CPU horse-power, and a well understood architecture.

-mark

On 24/06/2021 6:47 PM, Stephen Irons wrote:
> 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 
> http://www.padauk.com.tw/en/product/index.aspx
> 
> 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> wrote:
>> 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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