Oki OKIOFFICE44 Service Manual page 263

A3.1 R44 Circuit Diagram
A3.1.1 R44 Circuit Diagram)
1. Block diagram
The circuit diagram consists of the CPU, crystal oscillator circuit and reset signal generator.
Figure A3.1.1 shows the block diagram of CPU and the peripheral circuits.
2. Function
1) Crystal oscillator circuit
X1 is a 20 MHz crystal oscillator. The output wave is fed to the CPU through pin 73 and
74.
CLK (20 MHz) signal output from pin 71 is used as the system clock and output to IC2.
(IOGA3: input/output gate array).
2) CPU
CPU controls the following functions in addition to the basic processor.
Initial Reset Circuit
+5 V
Board Descriptions
• DMA (Direct Memory Access) control
• Interrupt procedure control
• A/D converter
• Bus state control
• Programmable pattern control
• 16 bit integrated timer pulse unit (ITU)
• Timing pattern control (TPC)
• Serial communication interface (SCI)
Address bus
Port C
(PC1/PC2)
IC1
RES
PWRDY-N
X1
XTAL
20 MHz
EXTAL
Related Signals of CPU (Figure A3.1.1)
A - 21
CPU
CK
OKIOFFICE 44 Serv. Man., P/N 59276801
Data/Address bus
Port A
Port B
M D-motor
Clutch
20 MHz