Tandy 1000 Technical Reference Manual

Tandy 1000
TYPE SN76494. SN76496
PROGRAMMABLE TONE/NOISE GENERATOR
TABLE 6 . FUNCTION TABLE
Technical Reference Manual
INPUTS
OUTPUT
CE WE
READY
L
L L
L
H L
H L
H
H H
H
This table
is valid when the
device is·
(I) not being clocked. and
(2) is initialIZed by pulling WE
BndCE high.
CPU interface to SN76494/SN76496
The microprocessor interfaces with the SN76494 by means of the eight data lines and three control lines (WE. CE
and READY). Each tone generator requires 10 bits of information to select the frequency and four bits of information
to select the attenuation. A frequency update requires a double-byte transfer. while an attenuator update requires a
single-byte transfer.
" no other control registers on the chip are accessed. a tone generator may be rapidly updated by initially sending
both bytes of frequency and register data, followed by just the second byte of data for succeeding values. The register
address is latched on the chip, so the data will continue g~ing into the same register. This allows the six most
significant bits to be quickly modified for frequency sweeps.
control registers
The SN76494 and SN76496 have eight internal registers that are used to control the 3 tone generators and the noise
source. During all data transfers to the SN76494 or SN76496, the first byte contains a three-bit field that determines
the destination control register. The register address codes are shown in Table 4.
TABLE 4 - REGISTER ADDRESS FIELD
DESTINATION
RO R1 R2 CONTROL REGISTER
0 0
0
Tone t Frequency
0 0
1 Tone 1 Anenuation
0
t
0
Tone 2 Frequency
0
t t Tone 2 Anenuation
t
0
0
Tone 3 Frequency
t
0
t Tone 3 Anenuation
1
1
0
Noise Control
1 1
1
Noise Anenuation
data formats
The formats required to transfer data are shown below.
[J
DATA I
........... .;..a."""""""'-;.;;;.. ....... ;...a....;..;.""'-""'- ....... '-' 0 x I Fe I Fl I F2 I F3 I F4 I F~
BIT 7 BIT 0 SECOND BYTE BIT 7
(SINGLE BYTE TRANSFER)
SHIFT
FB NFO NFl
MO M1
UPDATE ATIENUATOR (SINGLE BYTE TRANSFER)
n REG ADDR I DATA I
W RO I Rl I R2 NJ I Al I A2 I A3
BITO
BIT 7

Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200