Data Sheet

Rev. 3

4

AS2578 /B

March 1997

Memory Keys

The keys M1 to M3 are direct memory access keys and

the MEM key is used for abbreviated dialling.

13 numbers can be stored in on chip RAM. Each number

can contain up to 20 digits (including pauses).

If an EEPROM is connected to the serial bus, the content

of the RAM is written into the EEPROM when CE is

turned low indicating a power loss.

During programming multible pauses can be inserted by

pressing the LNR key.

Memory dialling is cascadable.

Mode Selection

The default mode (LD or MF) can be selected by the

MODE pin.

Furthermore, the mode can be selected by setting the

LM code (see setup menu). If no LM code is set, the

mode will be determined by the MODE pin.

When default LD mode is selected, a temporary change

to MF mode can be invoked by pressing * (AP = high,

AS2578 only) or Set, * , Set.

When the circuit is in temporary MF mode, each of the

following procedures revert it to default LD mode:

- pressing Set, * , Set ,

- pressing recall key (by further entries of the recall key

the signalling mode will toggle between MF and LD,

- by next On-hook.

RecallFunction

A recall activation will invoke a flash (timed loop break)

or a ground loop (GL) depending on the selected LM

code, which is stored in the external EEPROM (see

setup menu).

If no LM code is set, depressing the recall key will invoke

both a flash and a GL, however, in LD mode a Flash is

never executed.

If recall is the first entry in a digit string, it will be stored

in LNR RAM when digit(s) are entered after the recall.

If the recall key is depressed after a digit string has been

entered or dialled out, the recall will not be stored, and

subsequently entered digits will be stored in the LNR

RAM as the new number.

If pressing the recall key is not followed by digit entries,

the LNR RAM remains intact.

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.

The current contents of the RAM are overwritten by new

entries.

A manually entered number is automatically stored in the

LNR RAM. The capacity of the RAM is 30 digits. If a

number greater than 30 digits is entered, the LNR facility

will be inhibited (until new entries < 31 digits) and further

entries will be buffered in FIFO.

Postdialled digits, i.e. digits manually entered after LNR

has been invoked, are not stored in RAM but buffered in

FIFO.

Valid Keys

The keyscanning is enabled when CE or HS are high.

During setup the keyboard is disabled. 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 debounced. The

debounce time is 15 ms.

Mute Key

The mute key is only enabled when off-hook. Depressing

the mute key activates and deactivates (toggle switch)

the MUTE output, when internal mute is inactive, i.e. in

speech mode.

Any key entry overwrites a mute activated by the mute

key, and mute will be deactivated.

Centrex Keys (AS2578B only)

The alphameric keys accommodate easy use of centrex

services. The A, B, C and D keys are only valid in MF

mode and are not storable. Pressing one of these keys

will invoke the appropriate MF tones to be transmitted.

The centrex keys are not stored in the RAM, but are

buffered in the FIFO, and subsequently entered digits

are also buffered in the FIFO.

Pressing the recall key after a sequence including centrex

keys will reset the RAM counter, and subsequently

entered digits will be stored in the RAM. If MF select (Set,

* , Set) has been invoked once, then all susequently

digits/data will be buffered in the FIFO.