SA541 Datasheet, PDF (8/16 Pages) Sames – PULSE/DTMF SWITCHABLE DIALLERS

SA541
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
1
2
3
TBR
R2
4
5
6
LNR
R3
7
8
9
R4
∗
0
#
TBR:
LNR:
Timed Break Recall (Flash)
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)
Connected to:
V_SS
C1
C2
C3
V_DD
Dialling
Mode
LD
LD
LD
LD
DTMF
IDP(ms)
800
500
500
800
B:M Ratio
2:1
2:1
3:2
3:2
Table3: Dialling Mode Selection
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