@Aaron Thank you for these videos. I am designing & building a Eurorack synth as a hobby project. I'm not an EE and I would probably not have felt able to start this project without your videos, especially the ECE4450 lectures. Thanks!
There is a tiny mistake made in 10:15. The '2' in the code TMS9928/9 does not mean PAL version, the '9' does (in fact, I think the '8/9' in the schematic shows that both PAL and NTSC version of the VDP can be used here (with different video encoding vircuit, of course). The '2' in the code means 'component output', or in TI's terms, Y/R-Y/B-Y output. This is, interestingly enough, how the MC6847 chip of the Tandy Color Computer (1 & 2) output its video signal. If there is an '1' instead of a '2', the chip outputs composite video (TMS9918, TMS9918A, and TMS9118). There is no TMS9919 or TMS9919A or TMS9119, probably because of the complexity of the PAL encoder circuit.
I am messing around with the same chip. It appears that COMVID should be pulled down with something on the order of 470-ohms (the spec sheet is somewhat vague on the drive capacity of that pin.) By the way, what is the purpose of that 10K doing in between the base and emitter of that follower? On my system it appears to only increase the noise in the output. 😕
can't wait to see where you're taking us with this. I'm definitively hooked.
@Aaron Thank you for these videos. I am designing & building a Eurorack synth as a hobby project. I'm not an EE and I would probably not have felt able to start this project without your videos, especially the ECE4450 lectures. Thanks!
There is a tiny mistake made in 10:15. The '2' in the code TMS9928/9 does not mean PAL version, the '9' does (in fact, I think the '8/9' in the schematic shows that both PAL and NTSC version of the VDP can be used here (with different video encoding vircuit, of course). The '2' in the code means 'component output', or in TI's terms, Y/R-Y/B-Y output. This is, interestingly enough, how the MC6847 chip of the Tandy Color Computer (1 & 2) output its video signal. If there is an '1' instead of a '2', the chip outputs composite video (TMS9918, TMS9918A, and TMS9118). There is no TMS9919 or TMS9919A or TMS9119, probably because of the complexity of the PAL encoder circuit.
I am messing around with the same chip. It appears that COMVID should be pulled down with something on the order of 470-ohms (the spec sheet is somewhat vague on the drive capacity of that pin.)
By the way, what is the purpose of that 10K doing in between the base and emitter of that follower? On my system it appears to only increase the noise in the output. 😕
Oh hi! I've been watching your IMSAI video while trying to get my own IMSAI running.
@@Lantertronics 😂... small world!
I *think* the 10K is trying to do some kind of bootstrapping to increase the apparent input impedance of the BJT. Maybe?
@JohnsBasement You are a lifesaver! That 470 ohm pull-up DRASTICALLY improved the stability of the output.