ADV7123 on a propeller?

Comments

• SaucySoliton Posts: 487

  2019-08-14 14:59

  The propeller can output the pixel clock. This is done by selecting a PLL output mode on CTRA instead of PLL internal. Depending on the desired clock phase it might be necessary to use the inverted PLL output.
  
  forums.parallax.com/discussion/comment/1414279/#Comment_1414279
• jmg Posts: 15,144

  2019-08-14 20:02

  alatnet wrote: »

  Has anyone used a Video DAC on a propeller?
  Im looking into the ADV7123 and it supports 10 bits per color channel (though with propeller it would be just 2 bits and the rest on ground) and wondering if it's possible to use it instead of the resistor dac that is normally used.
  Looking into the schematic, the pixel clock is going to have to be exposed along with the H and V blank but would essentially replace the resistor dac while also opening up more possibilities in creating a rudementary gfx cards for probably a ton of microcontrollers including the propeller.
  Here's the site for the ADV7123: https://www.analog.com/en/products/adv7123.html#product-overview
  It seems to be the cheapest compared to the 7125 and 7120.

  
  Almost. See this thread
  https://forums.parallax.com/discussion/comment/1082063/#Comment_1082063
  The main problem with P1 is going to be feeding it enough pixels fast enough.
  Rayman paired the Video DAC with a SSD1963, which has large video RAM.
  
  Of course, P2 will do Video DACs for not much more $, and a whole heap less wasted pins !
  
• alatnet Posts: 80

  2019-08-14 22:00 edited 2019-08-14 22:04

  I was thinking of pairing it with a bit counter and 6 high speed ram chips, back and front buffer, 3 colors each.
  Then getting a flip flop and two bidirectional transceivers to be able to quickly flip between read output and write input on the two sets of ram chips when vsync occurs.
  So, direct access to the ram when writing data, either parallel or spi serial, while it is outputting the other to the vga.
  
  I got the idea from these two videos:
  Part 1:
  Part 2:
  
  Where he's using EEPROMS instead of ram but at the end of the second video he's manually swapping the EEPROMS.
  
  We certainly can drive the counter with the pixel clock from the propeller or even have an external oscillator to drive the pixel clock and have it output when vsync occurs and have the propeller tell the psudo gfx card to flip buffers on vsync.
• jmg Posts: 15,144

  2019-08-14 22:12

  alatnet wrote: »

  I was thinking of pairing it with a bit counter and 6 high speed ram chips, back and front buffer, 3 colors each.
  Then getting a flip flop and two bidirectional transceivers to be able to quickly flip between read output and write input on the two sets of ram chips when vsync occurs.
  So, direct access to the ram when writing data, either parallel or spi serial, while it is outputting the other to the vga.

  
  Yes, that could work, but that's now a lot of parts, and a lot of BUS wiring... ? may be smarter to wait for P2 in volume ?
  
  
• alatnet Posts: 80

  2019-08-14 22:16

  well, maybe. can probably use a qspi io expander to deal with all of the wiring for both addresses and data at a reasonable speed (though i dont know of any qspi io expander...) or a few spi io expanders.
• Rayman Posts: 13,855

  2019-08-16 20:36 edited 2019-08-16 20:41

  Depending on the goal, one might also consider pairing an EVE2 chip from FTDI with an hdmi or analog driver.... I think it should work...
  EVE2 is great for graphics that are more or less static....