Sharp FO-5700, Руководство по обслуживанию, Страница: 56 / 140

FO-5700U
5 – 12
(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.
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.
Fig. 3
IMAGE BUS
CONTROLLER
PROCESSING UNIT
IMAGE
BUS
BUFFER
E-FIFOAch
A0 ~ A2
D0 ~ D7
DRQTO
CODE
TABLE
ROM
CLKI
CKTST0
RTCL/RTCH
BRQT
SYSTEM
BUS
INTERFACE
PLL
CIRCUIT
DACKIN
E-FIFOBch
D-FIFOAch
D-FIFOBch
DBR
IMAGE DATA
DEMODULATING
CIRCUIT
PIXEL VARIATION
DETECTION
CIRCUIT
MICRO
PROGRAM
CONTROLLER
CONTINUOUS
EOL
DETECTION
CIRCUIT
MA/MD0 ~ 15
MA16 ~ 21
BACLN
DRQTI
DACKON
IMAGE BUS
INTERFACE
CODER & DECODER