NGPC Z80 instruction timing

[mic_]

To answer my own question: there's nothing strange about the Z80 clock or the instruction timings. The results I got was because the Z80 apparently can't run at full speed if the TLCS900H is accessing the shared RAM area at the same time

E.g. having a wait loop like this on the TLCS side:

Code:

vbw1:
   ld a,(Z80_COUNTER)  ; this address is in the shared RAM area
   ld a, (VBCOUNTER)
   cp a, w
   jr nz, vbw1

would make the Z80 run at approx 88% of it's normal speed.