SA541

sames

8/16

Simultaneous Key Depressions: If two keys are pressed simultaneously (i.e. a

second key is pressed before the first has been verified), neither key will be accepted

until both keys are released and the correct key is pressed again.

Table 2 indicates the keypad layout for the SA54X1 family.

C1

C2

C3

C4

R1

123TBR

R2

456LNR

R3

789

R4

∗

0#

TBR:

Timed Break Recall (Flash)

LNR:

Last Number Redial

Table 2: Keypad Layout

4.

Dialling Mode Selection

The dialling mode may be selected via the SELECT pin (pin 2) as detailed in Table

3. Four Loop-Disconnect options are available with different Interdigit pauses (IDP)

and Break:Make ratios. If the DTMF mode is selected, dialling will remain fixed in

the DTMF mode. However, if one of the LD modes is selected, the chip will be in

LD mode in the initial off-hook condition, but may be switched to DTMF by pressing

either the

∗ or # keys, provided that dialling is not in progress. If the ∗ or # keys are

pressed during LD dialling, they will be ignored.

Once in DTMF mode, depression of either the

∗ or # keys will cause the relevant

tone-pair to be output. Only digits entered prior to a DTMF switchover will be stored

and available for redialling (see Last Number Redial operation).

Once switched to DTMF, dialling will remain in this mode until either a Recall (Flash)

operation or until the device returns to the on-hook state.

Select (Pin 2)

Dialling

IDP(ms)

B:M Ratio

Connected to:

Mode

V

SS

LD

800

2:1

C1

LD

500

2:1

C2

LD

500

3:2

C3

LD

800

3:2

V

DD

DTMF

Table3: Dialling Mode Selection