Brother HL-820 Service Manual page 22

HL-1050
Fig. 2-6 shows the block diagram of the main PCB.
A S I C
CPU Core
(MB86831)
Oscillator (33.3MHz)
Reset Circuit
BUS
INT
Address Decoder
DRAM Control
Program + Font ROM
4.0 Mbytes
Timer
RAM
(4.0 Mbytes)
FIFO
Option RAM (SIMM)
CDCC Parallel I/O To PC
(max. 32Mbytes)
To PC
USB I/O
Option Serial I/O
(RS232C & RS422A)
Soft Support
EEPROM (512 x 8 bits)
EEPROM I/O
Motor Driver
Engine Control I/O
To Panel Sensor PCB
Fig. 2-6
II-6