Peripheral 3 Register
|Short Description||ABC/ACB Stereo, Internal Speaker, SpecDrum, Timex Video Modes, Turbo Sound Next, RAM contention and [un]lock 128k paging.|
(R/W) 0x08 (08) => Peripheral 3 setting:
bit 7 = Unlock(1)/lock(0) port $7FFD paging (read 1 indicates port $7FFD is not locked) bit 6 = 1 to disable RAM and I/O port contention (soft reset = 0) bit 5 = AY stereo mode (0 = ABC, 1 = ACB) (hard reset = 0) bit 4 = Enable internal speaker (hard reset = 1) bit 3 = Enable 8-bit DACs (A,B,C,D) (hard reset = 0) bit 2 = Enable port $FF Timex video mode *read* (hides floating bus on 0xff) (hard reset = 0) bit 1 = Enable Turbosound (currently selected AY is frozen when disabled) (hard reset = 0) bit 0 = Implement Issue 2 keyboard (port $FE reads as early ZX boards) (hard reset = 0)
The Timex modes are operational even when bit 2 is set to zero, you can still write to port $FF with desired mode changes. Bit 2 does only enable readability of port $FF.
When loading 48k SNA files through NextZXOS, be aware it does lock down many features of Next to better simulate ZX48 machine, including lock of Memory Paging Control ($7FFD / 32765) paging feature. If you are using 48k SNA file for convenience, but you are actually using full ZX Next features, make sure you enable/unlock all relevant bits, before using the particular feature.