AS2540Q AMSCO [austriamicrosystems AG], AS2540Q Datasheet - Page 8

• Manufacturer Part Number: AS2540Q
• Description: Remote Controlled Single-Chip-Telephone
• Manufacturer: AMSCO [austriamicrosystems AG]

Data Sheet AS2540
<Line Event> Message
Protocol
Line Events
AS2540 has 3 inputs, namely MHS (Manual Hook Switch),
EHS (Electronic Hook Switch) and RFD (Ring Frequency
Detector), which sense the state of the two hook-switches
and discriminate an applied ring signal. The MHS is
connected to the manual hook switch which is operated by
the handset and the EHS is connected to an electronic
hook switch which is operated by the CPU. Whenever the
state of these inputs changes, AS2540 immediately sends
<LineEvent> to the CPU after a debounce time. MHS and
EHS up-debouncing lasts 15ms, down-debouncing lasts
85ms. RFD start to discriminate the ring frequency
immediately but will send a <LineEvent> message with a
delay of 102ms. A status change of MHS and EHS pins
must not change the momentary selected path of the
speech network.
The <LineEvent>-message is sent without consideration of
the momentary activities of AS2540 in order to meet PTT
requirements (e.g. line break signalling). The code for the
<LineEvent>-message is chosen with regard to the
minimum current consumption in order to operate the
optocouplers. Pending <Ack>-messages will be queued
after the <LineEvent>-message. An already running
transmissions of <Ack> will not be interrupted and
<LineEvent> will be sent afterwards in this case.
-
AS2540 always starts up in backup mode and is prepared
to act like an independent dialler. <LineEvent> is sent to
the CPU and AS2540 remains in back-up mode until any
Revision 3.1
<LineEvent> message format
MSB
b
b
1
0
Mode transitions
7
7
b
b
1
0
6
6
b5
b
1
0
5
b
1
1
1
1
1
1
1
4
Idle
b
1
1
1
1
1
1
1
3
BM
b2
1
1
1
1
1
1
1
MPM
b1
10
10
10
10
10
10
1
Idle
LSB
b0
1
1
1
1
1
1
1
valid ring signal detected
no ring signal
manual hook switch - off-hook (pin MHS)
manual hook switch - on-hook (pin MHS)
electronic hook switch - off-hook (pin EHS)
electronic hook switch - on-hook (pin EHS)
valid message is sent from the CPU. This makes sure that
a non-operable CPU does not disable basic dialling
functions.
-
A watchdog timer is started after <LineEvent> and is reset
whenever AS2540 receives a message from the CPU via
the serial interface. If the CPU does not send any further
valid message within 2400ms, AS2540 goes back into
back-up mode, immediately locks the UART and remains in
backup mode till next on-hook.
Dialling Functions
DTMF
The DTMF generator provides 8 frequencies (in Hz):
Mode transition
697+1209
770+1209
852+1209
941+1209
Status
1
4
7
1
4
7
*
1
4
7
*
*
697+1336
770+1336
852+1336
941+1336
austriamicrosystems
2
5
8
0
2
5
8
0
2
5
8
0
MPM
697+1477
770+1477
852+1477
941+1477
BM
3
6
9
#
3
6
9
#
3
6
9
#
Status of AS2540
Remark
Page 8 of 18