Sharp FO-4700 Service Manual page 103

(9) CODEC block
This block is composed of CODEC, LS374 and LS244 in order to de-
modulate the contracted image data of the draft read with the scanner
and the letter image transmitted in the DMA mode from the system
memory.
1) HD813201F (IC12) ... pin-80, 6FP (CODEC)
It operates at 16 MHz corresponding to the crystal oscillator (X2) 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: IC16) 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
CONTROLLER
PLL PROCESSING UNIT
CIRCUIT
E-FIFOAch
E-FIFOBch
CODE
TABLE
ROM
D-FIFOAch
D-FIFOBch
DBR
CODER & DECODER
2) HD74LS374 (IC18) ... pin-20, SOP
The data hold time during writing from main CPU to HD813201F is as-
sured.
3) HD74LS244 (IC20) ... pin-20, SOP
When the main CPU reads the inner register of HD813201F, it will read
the data through this buffer.
MICRO
PROGRAM
IMAGE DATA
DEMODULATING
CIRCUIT
PIXEL VARIATION
DETECTION
CIRCUIT
Fig. 3
5 – 11
FO-4700TH
FO-47A4
IMAGE BUS
INTERFACE
BRQT
BACLN
IMAGE BUS
DRQTI
CONTROLLER
DACKON
MA16 ~ 21
IMAGE
BUS
BUFFER
MA/MD0 ~ 15
CONTINUOUS
EOL
RTCL/RTCH
DETECTION
CIRCUIT