Epson PX-8 - Speaker Circuit

REV.-A
2.13 Speaker Circuit
A cone speaker is built in on the back side of the MAPLE board. An external speaker can be also
connected as required.
(1) I
nput signal
The
following three signals are input to the speaker circuit:
•
Microcassette read signal- may be a sound source.
• Slave
CPU 6303 output.
• Expanded interface SPI signal.
(2)
Output control
The output to the speaker is controlled by the slave CPU 6303 via its port 17 as follows:
Port 1 7 level Control
High Enables the speaker circuit.
Low Disables the speaker circuit.
• The
output level to the speaker can be adjusted by a variable resistor.
• The internal speaker is
automatically switched to the external speaker when the speakel
cord
jack is connected with CN 11.
(3) Speaker
The
built-in speaker is a 200 mW, 8 ohm cone speaker with a frequency range from 600 Hz to
10,000 Hz.
Note: The BEEP command can specify up to 2500 Hz.
2.13.1 Circuit Operations
The speaker circuit includes an operational amplifier (NJM 386, 8B) whose operation voltage is
controlled by the slave CPU 6303 via port 17. When port 17 is at the high level, the operational
amplifier is activated. See Fig. 2-115.
SPI (Speaker Input from option unit)
8 9
...----CK78 From slave CPU 6303, port 16 (pin 19)
RDSP (Microcassette read data)
From slave
CPU 6303, port 17 (pin 20)
EXSP J '2 SP OUT
O
CN 11
1".0 fXSPG 1
33)J m
:IOV C5 SP~rr1
tl---'\N'V-'+=-~:""":""=-:""""_--'::.L."'-<.."..,.~"::"(..:.J4 33}J 10 V ~ SPGo-? llJ
Fig. 2-115 Circuit Operations
2-111