U3750BM Datasheet, PDF (14/20 Pages) TEMIC Semiconductors – One Chip Telephone Circuit

U3750BM
TELEFUNKEN Semiconductors
Timing of a Push Button
The information from a pressed push button or released push button is taken into account if it is still present during
at least two sampling times, T7.
Table 3 Timing of a push button
Clock Keyboard 2 ms, 2.2 ms
Minimum time – push button on
Minimum time – push button off
Min.
Typ.
Max.
Unit
14
24
34
ms
15.4
26.4
37.4
ms
24
24
34
ms
26.4
26.4
37.4
ms
The entries are debounced on both the leading and trailing edges for 34 ms or 37.4 ms according to the value of the
keyboard clock, and so the time remains less than 40 ms. At this time the information can be processed. If the informa-
tion is still present after more than 40 ms, it is only taken one time.
Serial Bus
The remote microcontroller is connected to the IC by 4 pins: C2, C3, C4, C5 (see figure 10).
Figure 10 Connection of the microcontroller to the U3750BM
C2 transmits the data, C3 the clock, C4 the enable signal, and C5 indicates the state of the dialer:
C5 = 0, dialer is busy
C5 = 1, dialer is free
Data is serially shifted in a 5-bit register during the positive going transition of the clock pulse. The positive going
transition of the enable signal validates the transmission.
14 (20)
Rev. A1: 16.07.1996