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IT- A4000
|
BUS DRIVER (74HC244) (1C805,807)
Buffer
to detect
the key input and the input signal (to detect receiving
etc.) from
the circuit. General
purpose
logic 74HC244
is used.
2-10- 2. Analog System and Telephone System
Main circuits are the speech network, dialer, ringer, receiving detection circuit, automatic hold releasing detection
circuit, CPC
detecting
circuits, voice
pass
system,
and
power
supply
system
circuit. As
most
of them
are
the
diversion from the current unit, only the differences from the current one will be described here (refer to the
circuit figure).
Dialer (IC902)
When
the power
supply
is on, DSP
conducts
the dial transmission.
However, the dialer is set to operate while the power supply is cut off. Thus, the dialer basically is not necessary.
The
prime dialer is used
due to the operation
while the power
supply is cut off.
Voltage Converter (IC103)
As IT-A4000
incorporates
CODEC,
a current
of —5V
is required.
Therefore, this unit uses
Voltage
Converter
ICL7660.
2-11. Test Program Style
Enter the test mode by starting up the power supply by pressing TIME/DEL
button and CLEAR
button at the
same time. LCD and LED are all lit after entering the test mode. This condition is defined as the test mode idle
condition.
Only the following keys are active in the idle condition.
ICM button (A, B, C), Clear button
When
the clear button is pressed in the idle condition, the unit exits the test mode
and returns to the initial
condition (RAM
check is not necessary).
General operations are possible after returning to the initial condition.
When
ICM button
is pressed, the tests corresponding
to each button
can be conducted (Light off LCD
and LED).
2-11-1. When ICM button A is pressed. ———>
Confirm the key input and the switch input.
Every time the button is pressed, the key input sound will be emitted from the speaker.
When
the switch is changed, the key input sound will be emitted from the speaker.
When
the batteries
are not inserted, "b"
will be displayed
at the left side on 7 segment
row.
When
the Clear button
is pressed, the unit returns
to the idle conditions.
2- 11-2. When ICM button B is pressed.
-——> Simple DRAM check .
20 pieces out of ARAM
1024 pieces are tested (approximately 2%).
Two
of the right side on the 7 segment
row
are counted
down
promptly (1-16)
(if the eighth ARARM
makes
the error,"7"
will be displayed).
When
the CLEAR
button
is pressed, the unit returns
to the test idle mode
condition.
Ra | ae
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