Sharp FACSIMILE FO-4500 Service Manual page 100

FO-4500H
(7) CODEC block
This block is composed of CODEC, LS374 and LS244 in order to
demodulate the contracted image data of the draft read with the scan-
ner and the letter image transmitted in the DMA mode from the sys-
tem memory.
1) HD813201F (IC14) ... pin-80, 6FP (CODEC)
It operates at 16 MHz corresponding to the ceramic oscillator (X4) of
16 MHz.
The image memory is commonly used as the page memory. The
image data of the draft read with the scanner in the page memory is
contracted by MMR, and is transferred to the system memory (DRAM:
IC7) by the DMA transfer function of CPU. Moreover, the image data
transferred in the DMA mode from the system memory are
demodulated with MMR, and are developed into the page memory.
A0 ~ A2
D0 ~ D7
SYSTEM
BUS
DRQTO
INTERFACE
DACKIN
CLKI
CKTST0
PLL PROCESSING UNIT
CIRCUIT
E-FIFOAch
E-FIFOBch
CODE
TABLE
ROM
D-FIFOAch
D-FIFOBch
DBR
CODER & DECODER
2) SN74LS374 (IC107) ... pin-20, SOJ
The data hold time during writing from main CPU to HD813201F is
assured.
3) SN74LS244 (IC104) ... pin-20, SOJ
When the main CPU reads the inner register of HD813201F, it will
read the data through this buffer.
MICRO
PROGRAM
CONTROLLER
IMAGE DATA
DEMODULATING
CIRCUIT
PIXEL VARIATION
DETECTION
CIRCUIT
Fig. 2
5 – 10
IMAGE BUS
INTERFACE
BRQT
BACLN
IMAGE BUS
DRQTI
CONTROLLER
DACKON
MA16 ~ 21
IMAGE
BUS
BUFFER
MA/MD0 ~ 15
CONTINUOUS
EOL
RTCL/RTCH
DETECTION
CIRCUIT