I'm trying to emulate an Amstrad CPC 464. I'm having trouble to understand how its Motorola MC6845 CRTC chip behaves on start-up. The boot ROM sets up the CRTC registers pretty early on, but if I assume all registers are 0 and just advance the internal counters as usual I get some strange behavior such as an immediate vertical sync.
So how does the actual CRTC behave when the system is started? I'm especially interested in the behaviour of hsync and vsync (though the data sheet says there is no hsync until register R2 is programmed).
One option that I can imagine, but have no way to confirm, is that the reset input RES of the CRTC is held active until all registers have been programmed. But that's just a wild guess.