This is replacement of original chip HAL10H8 or PAL10H8 in ZX128 and grey +2 models. Original chip contain controll fast/slow adress space, adressation of ports etc...
Original bugs in ZX128/+2 models:
a) after read from port 7FFD is writed to paging port data value from floating bus (unstable) and ZX crash.
b) if register "I" (IM2 table) is set to slow adress space then ULA show on TV output bugs in screen (raining effect/snow effect)
All this bugs can be removed if this chip is replaced with any other correct logic. For example GAL16V8 with same pinout.
Exist more firmwares for GAL:
New GAL16V8 as 100% replacement of HAL/PAL chip + fixed bugs :
- reading of port 7FFD is ignored = ZX no crach. Russian software use reading of this port for active turbo CPU mode (7MHz or faster).
- raining/snow effect is removed, but signal /REFRESH from CPU must be connect to pin 11 of new GAL chip. (This pin is on original HAL/PAL unused)
New GAL16V8 as replacement of HAL/PAL chip:
- reading of port 7FFD is ignored = ZX no crach. Russian software use reading of this port for active turbo CPU mode (7MHz or faster).
- raining/snow effect is removed, but signal /REFRESH from CPU must be connect to pin 11 of new GAL chip. (This pin is on original HAL/PAL unused)
- ports is fast (not contended). Only ULA port #FE is slow. Some demos,software will work with different timing (not 100% compatibility with original ZX timing)
Pentagon interface:
- my old memory upgrade for ZX128+2 to expand memory to Pentagon 512 mode. This hardware contain also HAL replacement and use more features.
PROFI interface:
- my last project - memory expansion for ZX128+2 to 1.5MB. Also replace HAL/PAL with selectable features.
GAL chips on pin 2 contain internal pull-down 10K after power-on. Adress line connect to this pin can be unstable. Better is use new PAL chip
