Re: RP2350 and Pico 2 - things missing

On 15/08/2024 18:05, Theo wrote:

James Harris <james.harris.1@gmail.com> wrote:

I have been looking forward to the Raspberry Pi Pico 2 for a while. The
increased speed will be welcome for one project I want to use it for.
>
However, according to what I've read there seem to be some missed
opportunities. Corrections would be welcome but AIUI:
>
* There are still no analogue /outputs/ - which I would have thought
would have been cheap and easy to provide.

 I suspect the analogue drive circuit is not that simple - would take
area and may compromise power, especially idle power.

I would have thought that such a circuit could be gated to reduce/remove power consumption. DAC needs far less circuitry (and no iteration) than ADC.

 You can get some of the way by using PWM and an external R-C network to low
pass filter the PWM.  Depends what kind of frequency you need.  Or there are
I2C DACs if you need a more accurate output.

I was hoping for analogue output pins initially in order to drive a VGA display. Would PWM work for that, do you think? My guess is that it would be too slow or jittery.
I have seen Pico set up to drive VGA through five resistors per colour. It may be a Pico reference design but there's a great version of it at
   https://vanhunteradams.com/Pico/VGA/VGA.html
The problem is that for three colour guns it takes fifteen pins!
Of course, external DACs increase the chip count and add latency and cost but I take your point.

 

* Although there are now 3 PIO units each one still has only 32 words of
program memory (which was very limiting in the Pico). I assume that
because the RP2350 is supposed to be software compatible meaning, among
other things, that it should run RP2040 PIO code.

 That does look to be the case.  Looks like the original RP2040 design
optimised them into a corner that's difficult to get out of.

Agreed. The curse of upwards compatibility. Though they could still have supported two different modes.
--
James Harris