that the input is valid. Keyboard bounce is ignored for 32ms after the initial key down is detected.
A key input is accepted if it is valid after this initial debounce time. This scheme allows any valid key
input to be recognized within 40ms of the initial key closure.
GND (Pin6)
Negative power supply pin.
Oscillator (Pins7 and Pin8)
The oscillator is formed by using a 480kHz ceramic resonator and two capacitors.
Make/Break Select (Pin9)
The Make/Break ratio may be selected by connecting this pin to either VDD or GND, Table 1 indicates
the two popular ratios from which the user can choose.
Table 1
Level of Pin9
VDD (Pin1)
GND (Pin6)
Make
40%
32%
Break
60%
68%
Mute Output (Pin10)
Pin 10 is the output of an open–drain N–channel transistor, It provides the logic necessary to mute
the network while the telephone line is being pulled.
Hook Switch Input (Pin15)
The Hook Switch input pin requires an external pull–up resistor to the positive supply. A VDD input
puts the circuit into On–Hook mode, while a GND inputs puts it into OFF–Hook or dialing mode.
Pulse Output (Pin16)
The Pulse Output pin is a N–channel open drain output for driving an external transistor, this external
transistor is used to switch the loop current in a telephone line.
Pin Connection Diagram
VDD 1
Test 2
Column Input 3
Column Input 4
Column Input 5
GND 6
OSC Input 7
OSC Output 8
16 Pulse Output
15 Hook Switch
14 Row Input
13 Row Input
12 Row Input
11 Row Input
10 Mute Output
9 Make/Break Select