H T 9 3 0 2 A /B /C /D
C1 C2 C3
R 4 * /T
R 4 * /T
These pins form a 4´4 keyboard matrix which can perform keyboard input detec-
tion and dialing specification setting functions. When on-hook (HKS=high) all the
pins are set high. While off-hook the column group (C1~C4) remains low and the
row group (R1~R4) is set high for key input detection.
I/O CMOS IN/OUT An inexpensive single contact 4´4 keyboard can be used as an input device.
Pressing a key connects a single column to a single row, and actuates the system
oscillator that results in a dialing signal output. If more than two keys are pressed at
the same time, no response occurs. The key-in debounce time is 20ms. Refer to
the keyboard information for keyboard arrangement and to the functional descrip-
tion for dialing specification selection.
The system oscillator consists of an inverter, a bias resistor and the necessary
load capacitor on chip. Connecting a standard 3.579545MHz crystal or ceramic
OSCILLATOR resonator to the X1 and X2 terminals can implement the oscillator function. The
oscillator is turned off in the standby mode, and is actuated whenever a key-
board entry is detected.
XMUTE is an NMOS open drain structure pulled to VSS during dialing signal
O NMOS OUT transmission. Otherwise, it is an open circuit. The XMUTE is used to mute the
speech circuit when transmitting the dial signal.
This pin is used to monitor the status of the hook-switch and its combination
with HFI/HDI can control the PO pin output to make or break the line.
HKS=VDD: On-hook state (PO=low). Except for HFI/HDI
(hand-free/hold-line control input), other functions are all disabled.
HKS=VSS: Off-hook state (PO=high). The chip is in the standby mode and
ready to receive the key input.
This pin is a CMOS output structure, which by receiving HKS and HFO/HDO
signals, control the dialer to connect or disconnect the telephone line.
PO outputs a low to break the line when HKS is high (on-hook) and HFO/HDO
PO O CMOS OUT is low. PO outputs a high to make the line when HKS is low (off-hook) or HFO is
high or HDO is high.
During the off-hook state, the pin also outputs the dialing pulse train in pulse
mode dialing. While in the tone mode, this pin is always high.
This is a three-state input/output pin, used for dialing mode selection whether
Tone mode or Pulse mode; 10pps/20pps.
MODE=VDD: Pulse mode, 10pps
MODE=OPEN: Pulse mode, 20pps
MODE=VSS: Tone mode
During pulse mode dialing, switching this pin to the tone mode changes the
subsequent digit entry to tone mode. When the chips are in tone mode, switch-
ing to the pulse mode will also be recognized.
3 September 30, 2002