AS2574B Datasheet, PDF (4/24 Pages) ams AG – 20 NUMBER ONE TOUCH DIALLER WITH SERIAL BUS FOR DISPLAY DRIVER

Data Sheet
Power On Reset
The on chip analogue power on reset circuit monitors the
supply voltage (V_DD). As long as V_DD remains below the
internal reference voltage, V (typically 1.2V), the
REF
oscillator is inhibited. When V_DD rises above V_REF, a reset
signal is generated to assure correct start-up, and the
oscillator is enabled.
The correct start-up/reset condition of the circuit is
guaranteed regardless of the absolute and chronologi-
cal rise time of V_DD, CD and HS inputs.
Line Supervision
In off-hook condition the device performs supervision of
the line current disconnects in the following manner:
Line disconnects (CD low) of less than 2 sec. are ignored
and the device continues operation.
Line disconnects of more than 2 sec. cause stop of
dialling and the circuit is switched to standby mode if HS
is high, otherwise the circuit will return to idle mode.
Valid Keys
A valid key is detected from the keyboard by connecting
the appropriate row to the column. This can be done
using an n x m keyboard matrix with single contacts.
Positive and negative edges of each contact are de-
bounced. The debounce time is 15 ms.
In idle state (on-hook) only the LS key is always valid
independent of the CD pin. When diode 5 is connected,
also the LNR, MEM, and M1 - 9 keys are valid entries
invoking ACP (automatic call progress).
Mute Key
Depressing the Mute key activates and deactivates
(toggle switch) the MT output, when internal mute is
inactive, i.e. when no data is being read from the RAM or
FIFO.
A change of the hook state will release the mute.
Mode Selection
The default mode (LD or MF) can be selected by the
diode option mode (diode 6).
When default LD mode is selected, a temporary change
to MF mode can be invoked by pressing the * key.
When the circuit is in temporary MF mode, each of the
AS2574B
following procedures revert it to default LD mode:
- pressing R key (all subsequently entered digits are
buffered in FIFO),
- by next On-hook.
Last Number Redial
LNR is a facility that allows resignalling of the last
manually dialled number without keying in all the digits
again. The LNR is repeatable.
A manually entered number is automatically stored in the
LNR RAM. The capacity of the RAM is 36 digits. If a
number greater than 36 digits is entered, the LNR facility
will be inhibited (until new entries < 37 digits) and further
entries will be buffered in FIFO. If more than 18 digits are
entered, the display will show the digit 19 and onwards.
Postdialled digits, i.e. digits manually entered after LNR
has been invoked, are not stored in RAM but buffered in
FIFO.
The current contents of the LNR RAM are overwritten by
new entries.
Memory Dial
An on chip RAM enables the dialler to store up to 20
numbers, each containing a maximum 18 digits/data.
The first 10 memories are accessible with 10 Direct dial
keys (M1 to M10) and another 10 memories (11 - 20) are
accessible by pressing the 2nd key before one of the
Direct dial keys or by pressing the MEM key and a digit
0 - 9 (abbreviated dialling).
Basic store procedure:
1 Press Enter key
2 Key in digits, including access code, pauses and recall
as appropriate (number is stored in LNR RAM)
3 Select location by keeping Enter key depressed while
entering the desired location (M1…M10, 2nd
M1…M10, or MEM 0…9)
4 Release Enter key to finish
5 Continue with 1, 2, 3 and 4 for storing further numbers.
Only the first 18 digits/data will be stored when copying
more than 18 digits/data in a memory.
Rev. 1
4
Jan. 1995