Difference between revisions of "Machine Type Register"

Revision as of 12:39, 11 November 2019

Number	$03
Readable	Yes
Writable	Yes
Short Description	Identifies timing and machine type.

A write to this register disables the bootrom in config mode

A write with bit 7 set will be accepted in any mode to change only display timing (bits 6-4).

Bit	Function
7	(W) 1 to allow changes to bits 6:4
7	(R) Next write to Enhanced ULA Palette Extension ($44) will affect colour byte: 0 = RRRGGGBB, 1 = p000000B
6-4	Display timing. %000-001: ZX 48k; %010: ZX 128k/+2 (Grey); %011: ZX +2A-B/+3e/Next Native; %100: Pentagon.
3	Reserved, must be 0
2-0	Machine type: %000: Config mode; %001: ZX 48k; %010: ZX 128k/+2 (Grey); %011: ZX +2A-B/+3e/Next Native; %100: Pentagon. Writeable only in config mode, may affect port decoding and enabling of some hardware.

@@ Line 5: / Line 5: @@
 |ShortDesc=Identifies timing and machine type.
 }}
-Only valid in [[IPL]] or config mode (0x0000-0x3FFF are mapped to the RAM instead of the internal ROM).
+A write to this register disables the bootrom in config mode
-A write to this register disables the IPL.
+A write with bit 7 set will be accepted in any mode to change only display timing (bits 6-4).
-A write with bit 7 set will be accepted in any mode to change only timing (bits 6-4).
 {| class="wikitable"
@@ Line 15: / Line 13: @@
 ! Function
 |-
-| 7 || (W) Lock Timing (change timing in any mode)
+| 7 || (W) 1 to allow changes to bits 6:4
 |-
 | 7 || (R) Next write to {{NextRegNo|$44}} will affect colour byte: 0 = RRRGGGBB, 1 = p000000B
 |-
-| 6-4 || Timing. %000-001: ZX 48k; %010: ZX 128k/+2 (Grey); %011: ZX +2A-B/+3e/Next Native; %100: Pentagon.
+| 6-4 || Display timing. %000-001: ZX 48k; %010: ZX 128k/+2 (Grey); %011: ZX +2A-B/+3e/Next Native; %100: Pentagon.
 |-
 | 3 || Reserved, must be 0
 |-
-| 2-0 || Machine type. %000: Config mode; %001: ZX 48k; %010: ZX 128k/+2 (Grey); %011: ZX +2A-B/+3e/Next Native; %100: Pentagon.
+| 2-0 || Machine type:
+%000: Config mode; %001: ZX 48k; %010: ZX 128k/+2 (Grey); %011: ZX +2A-B/+3e/Next Native; %100: Pentagon.
+Writeable only in config mode, may affect port decoding and enabling of some hardware.
 |}