NMOS version of Z80DMA chips not contain reset feature and some time can block ZX. For example if DMA transfer timing is set incorrect, then ZX ula have problems with timing video output... During blocked ZX is ignored ZX reset and user must disconnect power supply for full restart DMA.
CMOS version of Z80DMA chips contain reset feature, but need some extra logic for reset DMA. My latest version of DATA-GEAR(not on my web page) contain this logic.
