ACT apricot - Page 46

SYSTEM BOARD
Sound Generation
The Apricot uses the Texas Instruments SN 76489 sound
generator, which consists of the following major
components:
1. Three programmable tone generators, each with
associated control registers. (Tone generators I, 2 and
3).
2. A single programmable noise generator with
associated control registers.
3.
An 8-bit parallel interface for transferring data from
the data bus to the control registers.
4.An Audio
output buffer stage.
Within the BIOS, the sound generator is used for keyclick
(using
the noise generator) or the "bell" tone (using one of
the tone generator channels).
Systenn ~ennory
Address (hex)
Utilisation
00000 - 3FFFF
Standard RAM
40000 - EFFFF
RAM Expansion
FOOOO - FOFFF
Screen Buffer
F1000 - F7FFF
Unused
F8000 - FBFFF
Unused
Feooo - FFFFF
Bootstrap ROM
The standard System RAM consists of 32 64k x 1 bit
DRAMs, arranged in two blocks of 128Kbytes.
The RAM expansion is by way of the Expansion Sockets.
The Screen Buffer RAM is located in two separate Static
RAM
units.
The boot PROMs are 2 2764 PROMs.