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From: piglet <erichpwagner@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: port pins
Date: Thu, 12 Sep 2024 20:13:11 -0000 (UTC)
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Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
> piglet <erichpwagner@hotmail.com> wrote:
>> john larkin <jl@650pot.com> wrote:
>>> Something I've wondered about:
>>> 
>>> Suppose we have a c program running on some little uP, and it has some
>>> integer variable value, 8 or 12 bits or something, and wants to drive
>>> a parallel DAC off-chip.
>>> 
>>> The msb...lsb bits of the variable obviously have to get to the right
>>> pins of the DAC.
>>> 
>>> So, in general, how does one pick the physical i/o port pins on the
>>> uP, to get the order right? The PCB layout is easiest if we just wire
>>> the DAC to the handiest port pins.
>>> 
>>> One could test and bit-bang each bit and port individually, and then
>>> strobe the DAC, but that's inelegant.
>>> 
>>> In the RP2040 chip, one can apparently write to a register in a
>>> PIO/state machine block, where each bit of the register can be
>>> assigned to drive a physical port pin. I think there are some
>>> constraints on the selected pins.
>>> 
>>> 
>>> 
>> 
>> I didn’t know that now exists - but sounds super useful. Would have saved
>> much headache if it had been around years ago.
>> 
> 
> We sometimes use the LPC804, which has a gigantic pin mux—you can
> effectively put any function on any pin. IIRC reset and isp are a bit
> special, but all the gpio and built-in peripheral functions can be
> configured any way you like. 
> 
> Cheers 
> 
> Phil Hobbs 
> 

Many thanks for the tip! Currently all my projects are AVR and PIC but the
M0 could be next step up.

-- 
piglet