Yes hsyncs are always on, apparently they even appear in the mic signal when SAVEing programs to tape.kpalser wrote:I might be getting things a bit backward but I interpret Grant's fourth point as simply meaning that only HSYNCs are always being generated. And the loss of sync by the CRT in fast mode is from the user's code/key presses blocking the generation of the VSYNC, which prevents TV frames being drawn.
This should be easy to prove. Like have a program wait for a new frame, then run in FAST mode for a little while (short enough to not last outside top / bottom border area, long enough to last a number of hsync periods). I'm 99,99% sure this would have 0 effect on horizontal synchronization since the ULA takes care of that. A smart programmer might even takes this into account, and write some code that's mostly in FAST mode, but keeps TV sync (hor. and vert) and perhaps even display image every X frames.
So you're talking about vertical sync only which is software-generated like on the ZX80. Personally I don't see much point in adding hardware for that: if FAST processing takes long enough to last entire frames or longer, and there's nothing to look at anyway in the mean time, what's the problem with a little flicker to announce "I'm back" ?
AFAIK there's no -significant- difference between ULA versions other than the well known back porch issue.