IBM 5150 PC Technical Reference (6025005, August, 1981) (PDF)

Speaker Interface
The sound system contains a small permanent magnet 2-1/4" speaker.
The speaker can be driven from one or both of two sources. The
sources are:
1. An 8255A-5 PPI output bit. The address and bit are defined in
the I/O Address Map pages 2-23 and 2-24. ~
2. A timer Channel Clock out where the output is programmable
within the functions ofthe 8253-5 timer with a 1.19 Mhz clock
input. The timer gate is also controlled by an 8255A-5 PPloutput
port bit. Address and bit assignment are in the I/O Address
Map pages 2-23 and 2-24.
PPI BIT 1,1/0 ADDR x'0061'
1.19 MHz LOW
TO
,..--------, AND DRV PASS
CLOCK
SPEAKER
TIMER CLKOUT 2
FILTER
IN 2
PPI BIT 0, I/O ADDRESS X'0061'
Figure 10. SPEAKER DRIVE SYSTEM BLOCK DIAGRAM
Channel 2
ITone generation for Speaker!
GATE 2 - Controlled by 8255A-5 PPI Bit
(See I/O Map)
CLKIN2 -1.19318MhzOSC
CLK OUT 2 - Used to drive Speaker
- Used to write data on the Audio
Cassette
Speaker Connection - 4 Pin Berg Connector, Refer to
System Board Diagram page 2-13 for speaker connection.
PIN
FUNCTION
1 DATA
2 KEY
3 GROUND
4 +5 VOLTS
2-22