Standard Bitmap Mode

Introduction[edit | edit source]

Standard Bitmap Mode is an official Graphics Mode for the Commodore 64. It is sometimes referred to as High Resolution (HiRes) Mode. The mode allows for pictures of up to 320 x 200 pixel resolution and 16 colors across the screen. However, there are limitations on how the colors are implemented.

Implementation[edit | edit source]

In Control Register 1 ($d011) bit 6 (ECM) must be cleared and bit 5 (BMM) must be set. In Control Register 2 ($d016), bit 4 must be cleared. Table 1 highlights these bits.

Table 1 - VIC-II Control Registers
Hex Address	Dec Address	Type	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0	Contents
$D011	53265	Register	RST8	ECM	BMM	DEN	RSEL	YSCROLL			Control Register 1
$D016	53270	Register	-	-	RES	MCM	CSEL	XSCROLL			Control Register 2

Standard Bitmap Mode is 1 of 5 legal graphics modes achievable by the VIC-II; the others being combinations of the bits ECM, BMM and MCM. Table 2 shows the possible graphics modes available from the VIC-II.

Table 2 - Graphics Modes VIC-II Bit Combinations
Mode	ECM	BMM	MCM	Result
0	0	0	0	Standard Character Mode
1	0	0	1	Multicolor Character Mode
2	0	1	0	Standard Bitmap Mode
3	0	1	1	Multicolor Bitmap Mode
4	1	0	0	Extended Background Color Mode
5	1	0	1	Extended Background Color Multicolor Character Mode (invalid)
6	1	1	0	Extended Background Color Standard Bitmap Mode (invalid)
7	1	1	1	Extended Background Color Multicolor Bitmap Mode (invalid)

Characteristics[edit | edit source]

A Standard Bitmap Mode picture consists of 1 High Resolution bitmap of maximum size 320 x 200 pixels. Each 8 x 8 pixel character location can contain 2 different colors: 1 color is defined per character location, and 1 color is defined for the background. All 16 colors can be used.

Technical

The memory required to hold the data for a bitmap is relatively large. A 320 x 200 pixel image is made of 64,000 pixels. This requires 64 kilobits, or 8 kilobytes, of data. The additional color data required for an image this size is 1 kilobyte and is stored in Screen RAM; as it is not utilised conventionally in this mode. The lower nibble (bits 0-3) of each byte defines the background color, and the higher nibble (bits 4-7) defines the foreground color.