CMX850L8 View Datasheet(PDF) - CML Microsystems Plc
Part Name
Description
MFG CO.
'CMX850L8' PDF : 103 Pages View PDF
Communications Controller
CMX850
CASDET Register b0: Detect (read-only)
In CAS Tone Alert mode, this bit shows when valid CAS tones are being received, see figure 7a. In
FSK Receive mode it shows when valid FSK tones are being received, see figure 7b. This bit can
be monitored during a CLI message transaction to minimise falsing, as described in section
1.5.13.6.
b0 = 1 FSK signal or CAS tone pair present
b0 = 0 FSK signal or CAS tone pair not present
1.5.13.5
FSK Buffer Register (FSKBUF)
FSKBUF: Read-only. SFR Address $D1
All bits are cleared to 0 on reset.
Bit:
7
6
5
4
3
2
1
0
FSKBuffer Bit 7
FSK Buffer Bits 6-0
or
FSK Demodulator
O/P
FSKBUF Register b7: FSK Buffer Bit 7 or FSK Demodulator Output
When using FSK bit mode, this bit is permanently connected to the FSK demodulator output. In
byte mode, this bit will only be valid when a valid byte has been received. This bit will then hold bit
7 of the received byte until it has been read by the user, then the bit will become indeterminate until
the next valid byte is stored.
FSKBUF Register b6-0: FSK Buffer Bits 6-0
These bits are only valid when FSK byte mode is enabled and the interrupt status bit (CASDET b1)
is high to indicate that a valid FSK byte has been received. The received byte is stored in FSKBUF
b7-0 until it is read by the 8051 µC (see section 1.5.13.3).
1.5.13.6
Example of Using the Detector for Off Hook operations
The CASDET block uses the VBIAS generator and line input amplifier within the modem, but is otherwise
independent of the modem operation. On receipt of a valid CAS Tone Alert, it will be necessary for the 8051
µC to “wake up” the modem and sent the necessary acknowledgement. In this example FSK data is sent
from the Central Office, so either the modem or the alternative FSK demodulator can be used for the
subsequent data reception. If it is not known whether FSK or DTMF is being used for the data transfer, then
the modem can be set to receive DTMF while the CAS /FSK Detector is set to Mode 1 to receive FSK. An
example of a message transaction is shown in figure 7c.
Signals originating
from far end CPE
and Central Office
far voice
Signals originating
at near end CPE
A
CAS
B
ACK
C
D
FSK data
E
far voice
near voice
F
A.
Normal conversation with both near and far end voice present.
B.
Central Office mutes far end voice, sends CAS and becomes silent.
© 2003 CML Microsystems Plc
56
D/850/6
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