Table 2 : DTMF Output Frequency.

Key Input

Standard Frequency

Actual Frequency

% Deviation

ROW

1

2

3

4

697

770

852

941

699.1

766.2

847.4

948.0

+ 0.31

– 0.49

– 0.54

+ 0.74

COL

1

2

3

1209

1336

1477

1215.9

1331.7

1471.9

+ 0.57

– 0.32

– 0.35

PACIFIER TONE OUTPUT/CHIP DISABLE

INPUT

Output. Pin 11. The pacifier tone provides audible

Figure 6 : Typical Spectral Response.

feed-back, confirming that the key has been prop-

erly entered and accepted. A 500 Hz square wave

is activated upon acceptance of a valid key input, af-

ter the 32 ms debounce time. The square wave ter-

minates after a maximum of 30 ms or when the valid

key is no longer present. In pulse mode, all key en-

tries activate the pacifier tone. In tone mode, any

non-DTMF key (LND, FLASH, MEM, PROG) entry

activates the pacifier tone. When programming the

chip, all valid key entries activate the pacifier tone in

either pulse or tone mode.

The CHIP DISABLE is an input. When pin 11 is

switched low through a resistor (10 K to 100 K), the

MK53761 is enabled. When pin 11 is switched to V+

through the resistor, all keypad inputs are pulled

high, and the MK53761 will ignore all keypad inputs.

When the chip is disabled, it will not dial, and it can-

not be programmed. The chip can only be disabled

when the circuit is inactive (not dialing) and Pin 12

is switched high.

MUTE OUTPUT

Output. Pin 12. This pin is the MUTE OUTPUT for

both tone and pulse modes. Timing is dependent

upon mode.

The MUTE OUTPUT consists of an open drain N-

channel device. During standby, the output is high

impedance and generally has an external pullup re-

sistor to the positive supply.

In the tone mode, MUTE OUTPUT is used to re-

move the transmitter and the receiver from the net-

work during DTMF signaling. During dialing, MUTE

OUTPUT is active continuously until dialing is com-

pleted. MUTE OUTPUT goes active when any key

is pushed.

In the pulse mode, MUTE OUTPUT is used to re-

move the receiver and the network from the line. Dif-

ferent circuitry is required for tone and pulse muting

externalto the IC and applicationsusing both modes

would not necessarily share circuitry. MUTE OUT-

PUT timing is shown in Figure 8 for pulse mode sig-

naling and Figure 7 for tone mode signaling. MUTE

OUTPUT is active during each digit, and not active

during the interdigit time. In both tone and pulse

modes, MUTE OUTPUT goes active 40 ms before

PULSE OUTPUT for a FLASH. Figure 8 illustrates

the timing for this pin.

HKS

Input. Pin 17. Pin 17 is the hookswitch input to the

MK53761. This is a high-impedanceinput and must

be switched high for on-hook operation or low for off-

hook operation. A transition on this input causes the

on-chip logic to initialize, terminating any operation

in progress at the time. The signaling mode defaults

to the mode selected at pin 2.

PULSE OUTPUT

Output. Pin 18. This is an output consisting of an

open drain N-channel device. In either pulse or tone

mode, the FLASH key will cause a 560 ms output

pulse at pin 18.

MK53761

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