PULSE

R1

R2

R3

R4

MU/MFI

MIC+

1

2

3

4

5

6

7

8

9

10

28

27

26

25

24

23

22

21

20

19

MIC-

GTX

C1

C2

C3

MODE/PT

OSC

SEL

HKS

RXOUT

GND

V

DD

GDTMF

11

12

13

14

18

17

16

15

GRX

RXIN

I

REF

V

CC

LN

ILINE

LED

REG

PIN CONNECTIONS

PIN DESCRIPTION

C1, C2, C3, R4, R3, R2, R1

(Keyboard inputs, Pins 1, 2, 3, 25, 26, 27, 28)

The device interfaces with either the standard 2 of

8 with negative common or the single contact

(Form A) keyboard. Column 4 of the keypad is

connecting to ground.

A valid keypad entry is either a single Row con-

nected to a single Column or GND simultaneously

presented to both a single Row and a single Col-

umn. In its quiescent or standby state, during nor-

mal off-hook operation, the Rows are initialized at

at logic level 0 (GND). Pulling any row input low

enables the on chip oscillator. Keyboard scanning

then begins.

123

456

789

*

0#

Flas h

Tone /P ulse

Paus e

LND

Figure 1 : Keyboard Configuration

Scanning consists of Rows and Columns alter-

nately switching high through on chip pullups. After

both a Row and Column keys have been detected,

the debounce counter is enabled and any noise

(bouncing contacts, etc) is ignored for a debounce

period (TKD) of 32ms. At this time, the keyboard is

sampled and if both the Row and Column informa-

tion are valid, the information is buffered into the

LND location.

In the tone mode, if two or more keys in the same

row or if two or more keys in the same column are

depressed a single tone will be output. The tone

will correspond to the common row or common

column for which the two keys were pushed. This

feature is for test purposes, and single tone will not

be redialed. Also in the tone mode, the output tone

is continuous in the manual dialing as long as the

key is pushed. The output tone duration follows the

Table 1. When redialing in the tone mode, each

DTMF output is 90ms duration, and the tone sepa-

ration (inter signal delay) is 90ms.

Table 1 : Output Tone Duration

Key Push Time, T

Tone Output

T < 32ms

32ms < T < 90ms + Tkd

T > 90 ms + Tkd

No output, ignored by the device

90ms duration

Output duration = T - tkd

ST3917A - ST3917B

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