ST3917A datasheet(2/16 Pages) STMICROELECTRONICS

2 / 16 page

PULSE

MU/MFI

MIC+

MIC-

GTX

MODE/PT

OSC

SEL

HKS

RXOUT

GND

GDTMF

GRX

RXIN

REF

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

logic level 1 (VDD) and the columns are initialized

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

enables the on chip oscillator. Keyboard scanning

then begins.

123

456

789

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

2/16

ST3917A Datasheet(PDF) 2 Page - STMicroelectronics

ST3917A Datasheet(HTML) 2 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL