Atari 400 Hardware Manual

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Simple Display List Example: BASIC starts out in OS graphics mode 0
which displays 40 characters across by 24 rows. This is IR mode 2 wit n a
standard screen width. The OS sets up the display list near the top of
RAM with room for the character names at the top of RAM. On a 32 K-byte
machine, the display list would start at hex 7C20. The next three bytes
are hex 70's to create 24 blank lines. The next byte is a hex 42. The
4
tells the hardware to reload the memory scan counter with the following
address (7C40). This is the address of the data to be displayed. The 2
tells the hardware to display one line of IR mode 2 characters. The
next 23 bytes specify 23 more lines of mode 2 characters. Hex 41 is the
code for jumping and waiting until the end of the next vertical blank.
The address to jump to is 7C20, the start of the display list. TI1e next
960 bytes are the list of characters to be displayed, 40 bytes per line.
The OS must set up the display list pointer (DLISTH and DLISTL) to the
starting address of the display list (7C20). It also sets CHBASE to the
MSB of the address of the character set (EO).
This is a simple example because only one mode is used and the memory
scan counter is only loaded at one point. It is possible to have different
modes on different lines, change character sets and colors, etc. , as shown
in the example in Section IV.
11.19
ft.
7

Atari 400 Specifications

General

Manufacturer	Atari
Model	400
Type	Home Computer
Release Year	1979
CPU	MOS Technology 6502
CPU Speed	1.79 MHz
ROM	10 KB
Operating System	Atari OS
Keyboard	Membrane keyboard
RAM	8 KB (expandable to 48 KB)
Graphics	ANTIC and GTIA chips
Sound	4 channels
Display	RF output for connection to TV
Storage	Optional cassette tape drive or floppy disk drive
Ports	Cartridge
Display Resolution	320x192 (16 colors)