Sharp QD-101MM, Service Manual

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7. VARIOUS FUNCTIONS OF IC400(H8/3256 M.P.U)
IC400 is a microcomputer which is provided with a set of 16-bit free running timer and 2
channels of SCI in addition to 48K-byte PROM/2K-byte RAM.
7.1.Key data and various functions
The keys (DOWN, UP, SELECT, MENU, RESET) provided on the main body of QD-101MM
switches and selects the adjustment mode displayed in the LCD screen as well as gives the
direct commands to IC400.
1) DOWN
This key decreases the adjustment items selected by the select key, step by step.
2) UP
Being opposite to DOWN, the key increases the adjustment item, step by step.
3) SELECT
This key is used to select the adjustment mode in the menu screen which is displayed
by the MENU key.
Every push of this key can change the adjustment item, step by step.
4) MENU
This key is used to switch the menu screen.
5) RESET
This key is used to set the initial values of the computer. When this key is pressed,
the adjustment items are all returned to the initial statuses.
7.2.EEPROM control function
The EEPROM(IC413, 414) area is provided to write the timing set values of each computer
when it is connected to QD-101MM. The timing set values are written into EEPROM under the
following four conditions.
1. All resetting
2. Resetting
3. Power turn-off
4. The connected computer is changed.
Here, writing into EEPROM is executed only when the set value is changed.
7.3.Reset circuit
The circuit diagram is shown in MAIN CURCUIT No.4.
IC407(TL7705CPS-B) detects the power voltage, V
CPU
, of IC400 and its surrounding circuit,
and generates the RESET signal. If V
CPU
drops below the detection voltage (TYP4.5V) when
the power is turned off, IC407 shifts the level of the RESET signal to “Low”.
If V
CPU
rises to exceed the total voltage of the detection voltage V
S1
and hysteresis width
V
HYS1
(TYP15mV), IC407 starts charging the timing capacitor(C
t
) with a constant current.
After (T
P0
=1.3XC
t
X10[S]), IC407 shifts the RESET signal to “High” level. (See Fig. 8.)
IC411(S-8054ALB) detects the power voltage V
CC
to generate the power OFF signal. If V
CC
drops below the detection voltage V
S2
(TYP4. 15V) when the power is turned off, IC411 shifts
the power OFF detection level to “Low”.
If V
CC
rises beyond the total voltage of the detection voltage V
S2
and hysteresis voltage V
HYS2
(TYP200mV) when the power is turned on, IC411 shifts the power OFF signal to “High” level.
(See Fig. 9.)