MT88E45B
CB0 CB1 CB2
0/1
0/1
0/1
1
1
0
1
0
1
FSK
Interface
Function
Data Sheet
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/TIA 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.
Mode 1
Mode 0
Power Down. The MT88E45B is disabled and draws virtually no power supply
current.
Reserved for factory testing.
1
0
0
0
0
0
Table 1 - CB0/1/2 Functionality
The number of control bits (CB) required to interface the MT88E45B with the microcontroller depends on the
functionality of the application, as shown in Table 2.
Functionality Group
FSK (mode 0 or 1) and
Hybrid CAS only
(Non MEI compatible)
Control
s
CB2
Description
CB0 is hardwired to Vdd or Vss to select the FSK
interface.
CB1 hardwired to Vdd.
The microcontroller uses CB2 to select between the 2
functions.
CB0 is hardwired to Vdd or Vss to select the FSK
interface.
The microcontroller uses CB1 and CB2 to select between
the 3 functions.
CB0 is hardwired to Vdd to select FSK interface mode 1.
The microcontroller uses CB1 and CB2 to select between
the 4 functions.
FSK (mode 0 or 1),
Hybrid CAS,
Tip/Ring CAS
(MEI compatible or BT on-hook CLIP)
FSK (mode 1),
Hybrid CAS,
Tip/Ring CAS,
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)
CB1
CB2
CB1
CB2
CB0
CB1
CB2
All 3 pins are required.
Table 2 - Control Bit Functionality Groups
Functional Overview
The MT88E45B 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’.
Depending on the service, data delivery can occur
when the line is in the on-hook or off-hook state. In
most countries the data is modulated in either Bell
4
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.
In North America, Caller ID uses the voiceband data
transmission interface defined in the Bellcore
document GR-30-CORE. The terminal or CPE
(Customer Premises Equipment) requirements are
defined in Bellcore document SR-TSV-002476.
Typical services are CND (Calling Number Delivery),
CNAM (Calling Name Delivery), VMWI (Visual
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