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   PID: SoupGate-Win32 v1.05   
   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   
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