By default, the 1 kB of screen RAM or screen memory resides in memory at 1024-2023 ($0400-$07E7).
Use in BASIC[edit | edit source]
By using the BASIC command POKE, any of the 256 chars of the C64 can be placed in the video matrix.
This example will display the char A into the left upper corner (0 row, 0 column).
Limitations in extended color mode[edit | edit source]
By using the extended color mode the size of the character set is reduced. In this mode only 64 chars are available, because from 0, 64, 128, and 192 char value the chars (A-Z, 0-9 and punctuation marks) are printed with another background color.
Moving of screen RAM[edit | edit source]
The video matrix can be moved from its default location into other memory addresses with the following BASIC code:
POKE 53272,(PEEK(53272) AND 15) OR A
The memory that is addressed by variable A can be seen in the table below. The displaced screen memory has a handicap however, because the screen editor or the command code isn't viewable. That is a reason for using this feature only in programs.
|A||Start address of screen RAM|
|016||1024 ($0400) default|
Memory addresses[edit | edit source]
|Hex Address||Dec Address||Description|
|1 kB (1000 bytes) Screen RAM used for setting the characters to be displayed. The values placed in each location are "screen codes" (not PETSCII); the character displayed for a particular screen code is determined by the current character set. In the default character set values 128-255 display the same glyphs as values 0-127 but with inverted foreground and background colours. All of the character cells in the 40 columns by 25 row grid are directly accessible, e.g. |
|Sprite block register|
|$07F8||2040||Pointer for sprite 1 in memory block: Blockno.*64|
(e.g. sprite 1 in datasette I/O buffer $033C: Blockno. = 13 (13 * 64 = 832, in hex: $0340))
|$07F9||2041||Pointer for sprite 2 in memory block: Blockno.*64|
|$07FA||2042||Pointer for sprite 3 in memory block: Blockno.*64|
|$07FB||2043||Pointer for sprite 4 in memory block: Blockno.*64|
|$07FC||2044||Pointer for sprite 5 in memory block: Blockno.*64|
|$07FD||2045||Pointer for sprite 6 in memory block: Blockno.*64|
|$07FE||2046||Pointer for sprite 7 in memory block: Blockno.*64|
|$07FF||2047||Pointer for sprite 8 in memory block: Blockno.*64|