Subj : Re: RP2350 and Pico 2 - things missing To : James Harris From : Michael Schwingen Date : Sun Aug 18 2024 18:10:16 On 2024-08-18, James Harris wrote: >>> * 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. I suspect it takes (quite) some design effort to get it right (see the ADC on the RP2040), and requires analogue circuitry which is more difficult to implement in a given process than digital. Also, on-chip DACs are not too common in competitor parts - there are some that have it, but it is not standard. > I was hoping for analogue output pins initially in order to drive a VGA > display. That requires a *really fast* DAC. IIRC, standard VGA was ~25MHz pixel clock. For comparison, the STM32F407 DAC has a settling time of 3us (typical), meaning you can't do anything above ~300kHz. Getting a DAC to VGA speed (even at reduced resolution) requires quite some more design effort (and probably also chip area), and aside from analog VGA, there are probably few use cases. > Would PWM work for that, do you think? My guess is that it > would be too slow or jittery. I agree. > 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! Well, the new RP2350B has 48 instead of 30 GPIO pins available, so that should be anough for 6 bits / colour ;-) cu Michael -- Some people have no respect of age unless it is bottled. --- SoupGate-Win32 v1.05 * Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3) .