Re: port pins

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

--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics