Peripheral 3 Setting Register: Difference between revisions

Latest revision as of 14:47, 13 October 2025

Number	TBRegisterNumber::$08
Readable	TBRegisterReadable::Yes
Writable	TBRegisterWritable::Yes
Short Description	[[ShortDesc::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 {{#ask: PortNumber::$7FFD }} ($7FFD{{#ask: PortNumber::$7FFD |mainlabel=- |headers=hide |intro= / |?NumberDec#- }}) 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.

@@ Line 6: / Line 6: @@
 }}
 (R/W) 0x08 (08) => Peripheral 3 setting:
-   bit 7 = 128K paging enable (inverse of port 0x7ffd, bit 5)
+   bit 7 = Unlock(1)/lock(0) port $7FFD paging (read 1 indicates port $7FFD is not locked)
-          Unlike the paging lock in port 0x7ffd,
+   bit 6 = 1 to disable RAM and I/O port contention (soft reset = 0)
-          this may be enabled or disabled at any time.
+   bit 5 = AY stereo mode (0 = ABC, 1 = ACB) (hard reset = 0)
-          Use "1" to disable the locked paging.
+   bit 4 = Enable internal speaker (hard reset = 1)
-   bit 6 = "1" to disable RAM contention. (0 after a reset)
+   bit 3 = Enable 8-bit DACs (A,B,C,D) (hard reset = 0)
-   bit 5 = Stereo mode (0 = ABC, 1 = ACB)(0 after a PoR or Hard-reset)
+   bit 2 = Enable port $FF Timex video mode *read* (hides floating bus on 0xff) (hard reset = 0)
-   bit 4 = Enable internal speaker (1 = enabled)(1 after a PoR or Hard-reset)
+   bit 1 = Enable Turbosound (currently selected AY is frozen when disabled) (hard reset = 0)
-   bit 3 = Enable Specdrum/Covox (1 = enabled)(0 after a PoR or Hard-reset)
+   bit 0 = Implement Issue 2 keyboard (port $FE reads as early ZX boards) (hard reset = 0)
-   bit 2 = Enable Timex modes (1 = enabled)(0 after a PoR or Hard-reset)
-   bit 1 = Enable TurboSound (1 = enabled)(0 after a PoR or Hard-reset)
-   bit 0 = Reserved, must be 0
-https://www.specnext.com/tbblue-io-port-system/
+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 {{PortNo|$7FFD}} 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.