SA541 Datasheet, PDF (9/16 Pages) Sames – PULSE/DTMF SWITCHABLE DIALLERS

SA541
5. Last Number Redial (LNR)
The function of the on-chip LNR store is to automatically retain a manually dialled
number for redialling later. The capacity of the store is 32 digits. If a number longer
than 32 digits is dialled, redialling will be inhibited.
The LNR store has two features designed to assist the user,viz: Moving Cursor
Facility and Mixed Mode Dialling.
Moving Cursor Facility: This facility is provided to aid use in PABX applications,
where the user must first dial an access digit or digits, and then wait for a second dial-
tone before continuing dialling.
If the first digits of a new number dialled match the contents of the LNR store, then
pressing LNR button will dial out the remaining digits.
If there is a mismatch in the numbers then redial is inhibited until the next on-hook
and the LNR store will contain the new number.
If the user manually dials the first digit(s) matching those stored in LNR, and then
goes on-hook, the whole contents of the store will be retained.
Mixed Mode Dialling: In the case of a call which starts in LD mode and is switched
by the user (via the ∗ or # keys) to DTMF mode, only the digits dialled in LD mode
will be retained. Provided that the number of digits dialled in LD mode does not
exceed 32, the digits will be retained regardless of the number of DTMF digits
entered subsequently.
6. Earth Loop Recall (ELR) / Timed Break Recall (TBR) (Timed Flash)
The SA54X1 supports both TBR and ELR and offers a common operating protocol
in both cases.
After a Recall (Flash) operation, the dialling mode selected via the SELECT pin will
be restored. Only the digits dialled after the ELR/TBR operation will be retained in
the LNR store.
A TBR of 100ms (300ms on SA54X14) is generated when the TBR key is pressed.
The MASK output goes low in order to produce the line break. When in DTMF mode,
the MF OUT output also goes low for the duration of the break.
ELR is supported via the C3 pin. If this pin is connected to ground for a minimum
of 20ms during an ELR operation, the chip will offer the same operating protocol as
for TBR.
The ELR function may be achieved by use of the circuit shown in Figure 2, or by use
of a double contact switch.
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