I was reading up on various A/V mods for the Atari 2600, and I came across something interesting.
The TIA has 3 pins for luma and 1 pin for sync, and you're supposed to feed these into a resistor ladder to create an analog signal. The console already does this, and a really simple A/V mod takes the luma from right before it goes into the RF modulator and uses that. A more complicated mod grabs the signals straight from the TIA and puts them through its own resistor ladder. However, if you feed them into a buffer first (the schematic said CD4050, I guess a 74904 would be the same thing?) before the resistor ladder, the video signal is much sharper/cleaner visually.
Why? Is the TIA's output noisy or slow or something that the buffer filters it into a sharper 0/1 binary signal? The signals are open collector, so I dunno if that makes a difference.
I'm curious because I think up circuits all the time, and one of the things I was working out is how to drive a plain arcade RGB monitor using a DAC, but now I don't know if it's necessary to buffer the digital part of the signal first, before sending it to the DAC. Were buffered video circuits common in arcade games too?
The TIA has 3 pins for luma and 1 pin for sync, and you're supposed to feed these into a resistor ladder to create an analog signal. The console already does this, and a really simple A/V mod takes the luma from right before it goes into the RF modulator and uses that. A more complicated mod grabs the signals straight from the TIA and puts them through its own resistor ladder. However, if you feed them into a buffer first (the schematic said CD4050, I guess a 74904 would be the same thing?) before the resistor ladder, the video signal is much sharper/cleaner visually.
Why? Is the TIA's output noisy or slow or something that the buffer filters it into a sharper 0/1 binary signal? The signals are open collector, so I dunno if that makes a difference.
I'm curious because I think up circuits all the time, and one of the things I was working out is how to drive a plain arcade RGB monitor using a DAC, but now I don't know if it's necessary to buffer the digital part of the signal first, before sending it to the DAC. Were buffered video circuits common in arcade games too?