MT88E45
Advance Information
FSK
Interface
CB0 CB1 CB2
Function
0/1
0/1
0/1
1
1
0
1
0
1
Set by CB0 FSK Demodulation. Tip/Ring input (GS1) selected. DR/STD is DR.
Set by CB0 Hybrid CAS Detection. Hybrid Receive input (GS2) selected. DR/STD is STD.
Set by CB0 Tip/Ring CAS Detection. Tip/Ring input (GS1) selected. DR/STD is STD.
When the line is off-hook, a Bellcore Multiple Extension Interworking (MEI)
compatible Type 2 CPE should be able to detect CAS from Tip/Ring while the
CPE is on-hook because it may be the ACK sender. Tip/Ring CAS detection is
also required for BT’s on-hook CLIP.
1
0
0
0
0
0
Mode 1 Power Down. The MT88E45 is disabled and draws virtually no power supply
current.
Mode 0 Reserved for factory testing.
Table 1 - CB0/1/2 Functionality
The number of control bits (CB) required to interface the MT88E45 with the microcontroller depends on the
functionality of the application, as shown in Table 2.
Control
Functionality Group
FSK (mode 0 or 1) and
Description
s
CB2
CB0 is hardwired to Vdd or Vss to select the FSK
Hybrid CAS only
interface.
(Non MEI compatible)
CB1 hardwired to Vdd.
The microcontroller uses CB2 to select between the 2
functions.
FSK (mode 0 or 1),
Hybrid CAS,
CB1
CB2
CB0 is hardwired to Vdd or Vss to select the FSK
interface.
Tip/Ring CAS
The microcontroller uses CB1 and CB2 to select between
(MEI compatible or BT on-hook CLIP)
the 3 functions.
FSK (mode 1),
Hybrid CAS,
Tip/Ring CAS,
CB1
CB2
CB0 is hardwired to Vdd to select FSK interface mode 1.
The microcontroller uses CB1 and CB2 to select between
the 4 functions.
Power Down
(MEI compatible or BT on-hook CLIP)
FSK (mode 0), Hybrid CAS,
Tip/Ring CAS, Power Down
(MEI compatible or BT on-hook CLIP)
CB0
CB1
CB2
All 3 pins are required.
Table 2 - Control Bit Functionality Groups
Depending on the service, data delivery can occur
Functional Overview
when the line is in the on-hook or off-hook state. In
most countries the data is modulated in either Bell
202 or CCITT V.23 FSK format and transmitted at
1200 baud from the serving end office to the
subscriber’s terminal. Additionally in off-hook
signalling, the special dual tone CAS is used to alert
the terminal before FSK data transmission. BT uses
CAS to alert the terminal prior to FSK in both on-
hook (Idle State) and off-hook (Loop State)
signalling.
The MT88E45 is compatible with FSK and FSK plus
CAS (CPE Alerting Signal) based Caller ID services
around the world. Caller ID is the generic name for a
group of services offered by telephone operating
companies whereby information about the calling
party is delivered to the subscriber. In Europe and
some other countries Caller ID is known as Calling
Line Identity Presentation (CLIP). ETSI calls CAS
‘Dual Tone Alerting Signal’ (DT-AS), BT calls it ‘Tone
Alert Signal’.
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