Screen Memory

Defaults

The default screen location when you power on your Commodore 64 is 0400 to 07E7 (1024 to 2023 decimal).

Which is 1,000 bytes.

Video Bank

All graphics for the VIC-II are relative to the current video bank.

There are four video banks available to the Commodore 64.

Only one bank can be active at a time and each bank is 16KB in size. Which means the VIC-II can only access 16KB of graphics memory. Careful consideration should be in your design when choosing which bank(s) to use for your game or demo.

Address	Mask	Bank	Yields
DD00	%xxxxxx11	bank0	0000 - 3FFF
DD00	%xxxxxx10	bank1	4000 - 7FFF
DD00	%xxxxxx01	bank2	8000 - BFFF
DD00	%xxxxxx00	bank3	C000 - FFFF

How to change video banks

// Video Bank 0
LDA $DD00
AND #%11111100
ORA #%00000011
STA $DD00

// Video Bank 1
LDA $DD00
AND #%11111100
ORA #%00000010
STA $DD00

// Video Bank 2
LDA $DD00
AND #%11111100
ORA #%00000001
STA $DD00

// Video Bank 3
LDA $DD00
AND #%11111100
ORA #%00000000
STA $DD00

Character Memory

All addresses are relative to the video bank. For example, using Video Bank 1 and setting D018 to 0800 yields character memory being located at 4800.

Address	Mask	Type	Yields
D018	%xxxx000x	charmem	0000
D018	%xxxx001x	charmem	0800
D018	%xxxx010x	charmem	1000
D018	%xxxx011x	charmem	1800
D018	%xxxx100x	charmem	2000
D018	%xxxx101x	charmem	2800
D018	%xxxx110x	charmem	3000
D018	%xxxx111x	charmem	3800

Setting Character Memory and Screen Memory Location

The following KickAssembler macro makes it easy to switch banks. Just replace screen with the desired screen location and charset with the desired character set location.

LDA #[[screen & $3FFF] / 64] | [[charset & $3FFF] / 1024]
STA $D018