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A valid keypad entry is either a single Row con-
nected to a single Columnor GND simultaneously
presented to both a single Row and a single Col-
unm.
In its quiescent or standby state, during normal
off-hook operation, either the Rows or the Col-
umns are at logic level 1 (V
DD
). Pulling one input
low enables the on chip oscillator. Keyboard
scanningthen begins.
Scanning consists of Rows and Columns alter-
nately switching high through on chip pullups. Af-
ter both a Row and Column key have been de-
tected, the debouncecounter is enabled and any
noise (bouncing contacts, etc) is ignored for a de-
bounce period (TKD) of 32ms. At this time, the
keyboardis sampled and if both the Row and Col-
umn information are valid, the information is buff-
ered into the LND location. After scanning starts,
the row and column inputs will assume opposite
states.
In the tone mode, if two or more keys in thesame
row or if two or more keysin the samecolumn are
depressed a single tone will be output. The tone
will corresponds to the row or column for which
the two keyswere pushed. Thisfeature is for test-
ing purposes, and single tone will not be redialed.
Also in the tone mode, the output tone is continu-
ous in the manual dialing as long as the key is
pushed. The output tone duration follows the Ta-
ble 1. When redialing in the tone mode, each
DTMF output has 100ms duration, and the tone
separation(inter signal delay) is 100ms.
Table 1:
Output Tone Duration
Key-Push Time, T
T<= 32ms
Tone Output
No output, ignored by
one chipphone.
100ms Duration
32ms < = T < = 100ms +
Tkd
T > = 100ms + Tkd
Output Duration= T - Tkd
OSC
Output. Pin 5. Only one pin is needed to connect
the ceramic resonator to the oscillatorcircuit. The
other end of the resonator is connected to GND
(pin 8). The nominal resonator frequency is
3.579545MHz and any deviation from this stand-
ard is directly reflected in the Tone output fre-
quencies. The ceramic resonator provides the
time reference for all circuit functions. A ceramic
resonator with tolerance of
±
0.25% is recom-
mended
PULSE
Output. Pin 6. This is an output consisting of an
open drain N-Channel device. During on-hook,
pulseoutputpin is inhigh impedanceand onceoff-
hooked,it will be pulled high byexternalresistor.
MODE/PACIFIERTONE
Input (MODE). Pin 7. MODE determines the di-
aler’s default operating mode. When the device is
powered up or the hookswitch input is switched
from on-hook (V
DD
) to off-hook (GND), the default
determines the signalling mode. A V
DD
connec-
tion defaults to tone mode operation and a GND
connectiondefaults to pulse modeoperation.
When dialing in the pulse mode, a softswitch fea-
ture will allow a change to the tone mode when-
ever the * key is depressed. Subsequent * key in-
puts will cause the DTMF code for an * to be
dialed.. The softswitch will only switch from pulse
to tone. Afterreturning to on-hook and back to off-
hook, the phone will be in pulse mode. Redial by
the LND key or the MEM key will repeat the soft-
switch.
Output (PACIFIER TONE). Pin 7. In pulse mode,
all valid key entries activate the pacifier tone. In
tone
mode, any non DTMF entry (FLASH,
PROG, PAUSE,LND, MEM, E1, E2 and E3), acti-
vates the pacifier tone. The pacifier tone provides
audible feedback, confirming that key has been
properly entered and accepted. It is a 500Hz
square wave activated upon acceptance of valid
key input after the 32ms debounce time. The
square wave terminates after a maximum of
75ms or when the valid key is no longer present.
The pacifier tone signal is simultaneously sent to
earphone and the buzzer. The buzzer can be re-
moved withoutaffecting this function.
HKS
Input.Pin 8. This is the hookswitch input to the one
chip phone. This is a high impedance input and
must be switched high foron-hookoperationor low
for off-hook operation. A transition on this input
causes the on chip logic to initialize, terminating
anyoperationin progressat the time. The signaling
mode defaults to the mode selected at pin 7. Fig-
ures1 and2 illustrate thetiming for this pin.
GND
Pin 9 is the negative line terminal of the device.
Thisis thevoltagereference for all specifications.
RXOUT, GRX, RXIN
RXOUT (pin 10), GRX (pin 11) andRXIN (pin 12).
The receive amplifier has one input RXIN and a
non inverting output RXOUT. Amplification from
RXIN to RXOUT is typically 31dB and it can be
adjusted between 11dB and 41dB to suit the sen-
sitivity of the earphone used. The amplification is
proportionalto the externalresistor connectedbe-
tweenGRX and RXOUT.
FUNCTION PIN DESCRIPTION
(continued)
L3916A - L3926A - L3936A
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