Sharp MZ-700 Series Owner's Manual page 134

4.3.2 Signal system of the 8253
The 8253 includes three counters # 0, # 1 and # 2. Counter # 0 is used for sound generation, and
counter # 1 and # 2 are used for the built-in clock.
Counter # 0 is used as a square wave rate generator (MODE 3) and counter # 1 is used as a rate genera-
tor (MODE 2). Counter # 2 is used for the interrupt on terminal count (MODE 0).
A 895 kHz pulse signal is applied to counter # 0, which devides the frequency to the specified value
according to the note information. This divided signal is output to the sound generator.
Counter # 1 counts a 15.7 kHz pulse signal and outputs a pulse to OUT1 every 1 second. Counter
# 2 counts the output signal from counter # 1 and outputs a high level pulse to OUT2 every 12 hours.
Since OUT2 is connected to the interrupt terminal of the CPU, the CPU processes the interrupt every
12 hours.
8 2 5 3
O U T 2
C L K 2
D
7
O U T 1
D o
C L K 1
I N T
"MS K
^ y I N T 1
O U T 2
C L K 2
D
7
O U T 1
D o
C L K 1 «
B L N K ( 1 5 . 6 1 1 KHz)
O U T O
C L K O
D>AMP. ^ d
S P
- 8 9 5 K H z
32-