Difference between revisions of "Layer 2 RAM Page Register"

Revision as of 13:08, 11 November 2019

Number	$12
Readable	Yes
Writable	Yes
Short Description	Sets the bank number where Layer 2 video memory begins.

Bits 6-0 store the number of the "SRAM page" (ie, bank) used for the standard Layer 2 screen. The default is 8. Because the layer 2 screen is 48kiB, it actually occupies 3 banks, and the number set here is the first; so by default, it occupies banks 8-10. Then later NextZXOS does reconfigure both this and shadow bank to 9 (banks 9-11). (bit 7 is reserved, use always 0)

For shadow bank paging see Layer_2 and Layer 2 RAM Shadow Page Register ($13).

Note that this register uses the 16kiB bank method, so if you set Nextreg $12,$C if you need to read the contents via 8kb banks you would need to multiply x 2 (16k bank $0C is identical to 8k pages $18 and $19).

@@ Line 5: / Line 5: @@
 |ShortDesc=Sets the [[Memory map|bank]] number where Layer 2 video memory begins.
 }}
-Bits 5-0 store the number of the "SRAM page" (ie, [[Memory map|bank]]) used for the standard Layer 2 screen. The default is 8. Because the layer 2 screen is 48k, it actually occupies 3 banks, and the number set here is the first; so by default, it occupies banks 8-10. Then later NextZXOS does reconfigure both this and shadow bank to 9 (banks 9-11).
+Bits 6-0 store the number of the "SRAM page" (ie, [[Memory map|bank]]) used for the standard Layer 2 screen. The default is 8. Because the layer 2 screen is 48kiB, it actually occupies 3 banks, and the number set here is the first; so by default, it occupies banks 8-10. Then later NextZXOS does reconfigure both this and shadow bank to 9 (banks 9-11). (bit 7 is reserved, use always 0)
 For shadow bank paging see [[Layer_2]] and {{NextRegNo|$13}}.
-Note that this register uses the 16kb bank method, so if you set Nextreg $12,$C if you need to read the contents via 8kb banks you would need to multiply x 2 (16k bank $0C is identical to 8k pages $18 and $19).
+Note that this register uses the 16kiB bank method, so if you set Nextreg $12,$C if you need to read the contents via 8kb banks you would need to multiply x 2 (16k bank $0C is identical to 8k pages $18 and $19).