I Keyboard inputs may be connected to either a standard
keyboard, an inexpensive signal contact (Form A)
keyboard, or electronic input from a µC. A valid key entry
is defined by a single row being connected to a single
I, O A built-in inverter provides oscillation by means of an
inexpensive 3.579545 MHz crystal or ceramic resonator.
O The T/P MUTE is a conventional CMOS inverter that
pulls to VDD in the absence of keypad input and pulls to
VSS when an address keypad entry is sensed (excluding
the * and # keypads in pulse mode). When any keypad in
row 5 and column 5 is pushed, the mute out remains at
I Pull to VSS to enable tone mode. Pull to VDD to enable
pulse mode (10 ppS).
I Hook switch input. When pulled to high, chip is in on-hook
state (no operation). When pulled to low, chip is in off-
hook state (enabled for normal operation). This pin is
pulled to VDD by internal resistor.
Note: This pin operates in conjunction with the handfree
control pins; for further information see description of
handfree control pins below.
I B/M = 1: Break/Make ratio is 60:40.
B/M = 0: Break/Make ratio is 67:33.
This pin has no function in tone mode.
I Power input pins.
O The X MUTE is a conventional CMOS inverter that in tone
mode is active while a DTMF signal is being transmitted.
In pulse mode, this output remains low at all times.
Publication Release Date: August 1996