Samsung SCX-1100 Service Manual page 78

3-3-3 RESET CIRCUIT
This system is configured with PRIMARY RESET(/POR) of
Power Reset, Reset by WATCH DOG TIMER, external
PRIMARY RESET, and SECOND RESET(/_F_POR)
which was done AND. PRIMARY RESET SYSTEM is used
for resetting MAIN CONTROLLER(U15) when System
Power is authorized, and SECOND RESET resets FLASH
MEMORY(U7). Figure 15 below is BLOCK DIAGRAM
related to the reset of entire system.
When +3.3V reaches 3.1V so that system may operate,
POWER MONITOR(U13) moves to High(+3.3V) after
maintaining low(OV) in the degree of 50mS-200mS output
while monitoring it. This Reset signal is input into MFP
CONTROLLER(S3C46MOX(Jupiter3 : U15) right away,
and MFP CONTROLLER becomes awake. And it releases
/F_POR after MCLK 1 clock.
Samsung Electronics
3-3-3-1 POWER MONITOR ( U13 )
Since +3.3V power supplied to XC61FN3112MR is unsta-
ble, when it becomes 3.1V(3.038V~3.162V), it is checked
as the POWER FAILURE. And the output terminal of
XC61FN3112MRF becomes LOW(0V),it is applied to
S3C46MOX(Jupiter3)(U15), and RESET(LOW ACTIVE) is
operated When S3C46MOX(Jupiter3) Reset is cancelled,
FLASH
S3C46MOX(Jupiter3) is Reset together. Output terminal of
XC61FN3112MRF is pulled up 100KΩ in the structure of
Open drain.
3-3-3-2 WATCH DOG OUTPUT (/F_POR)
Since WATCH DOG TIMER, which is Programmable
Counter in S3C46MOX(Jupiter3) is set as disable for INI-
TIAL STATE, it shall be set as Disable so that it won't oper-
ate, and after it is initialized for operation, it shall be reused
by setting it Enable. When Watch Dog Reset occurs, it is
about 10mS depending on the value set at the initial stage.
And Counter value of Watch Dog Timer is changed by the
program. Reset signal (/F_POR,UI5-106) shall be generat-
ed, and entire system shall be Reset and initialized.
< Figure 13. POWER RESET BLOCK DIAGRAM >
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CIRCUIT DESCRIPTION
MEMORY connected to
Repair Manual
/F_POR of
3-19