Asic - Brother HL-720 - B/W Laser Printer Service Manual

1.3.2

ASIC

The ASIC is composed of a Cell Based IC and has the following function blocks.
(1) Oscillator circuit
Generates the main clock for the CPU by dividing the source clock frequency by
two.
(2) Address Generator
This controls the address buss by latching the AD buss signals with the ALE
signal.
(3) Address decoder
Generates the CS for each device.
(4) DRAM control
Generates the RAS, CAS, WE, OE and MA signals for the DRAM and controls the
memory refresh processing (CAS before RAS self-refreshing method).
(5) Interrupt control
Interrupt levels:
Priority High
Low
All the interrupts can be masked.
(6) Timers
The following timers are included:
Timer 1
Timer 2
Timer 3
(7) FIFO
A 10Kbit FIFO is includedrporated. Data for one raster is transferred from the
RAM to the FIFO by DMA transmission and is output as serial video data. The
data cycle is 6.13 Mhz.
9 TIMER 3 (Watch Dog)
8 MONITOR
7 FIFO
6 EXINT
5 TIMER1
4 BD
3 Spare
2 CDCC / BOISE / DATA EXTENTION
1 TIMER 2
16-bit timer
10-bit timer
Watch-dog timer
II-4