Other Circuits
,..-...,.,
Speaker Circuit
The sound system has a small, permanent magnet, 57.15 mm
(2-1/4
in.) speaker. The speaker can be driven from one or both
of two sources:
•
An
8255A-5 programmable peripheral interface (PPI) output
bit. The address and bit are defined in the
"I/O
Address
Map".
• A timer clock channel, the output of which is programmable
within the functions of the 8253-5 timer when using a
1.19-MHz clock input. The timer gate also
is
controlled by an
8255A-5 PPI output-port bit. Address and bit assignment are
in the
"I/O
Address Map".
PPI
Bit 1. 1/0 Address Hex
0061_
1.19
MHz
AND
Clock
Low
To
-
In2
Timer
Clock
Out
2
r---.
- Driver
t--
Pass
i'-'Speaker
-
Gate 2
Filter
PPI
Bit
O.
1/0 Address Hex 0061
Speaker Drive
System
Block Diagram
Channel 2 (Tone generation
for
speaker)
Gate 2 - Controller
by
8255A-5
PPI
Bit
(See
1/0 Map)
Clock In 2 - 1.19318 -
MHz
OSC
Clock Out 2 - Used
to
drive speaker
,..-...,.,
Speaker Tone Generation
System Board
1-25
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