am79r251 Advanced Micro Devices, am79r251 Datasheet - Page 21

• Manufacturer Part Number: am79r251
• Description: Intelligent Subscriber Line Interface Circuit Islic
• Manufacturer: Advanced Micro Devices

Operating Modes
Table 1.
Note:
1. In these modes, the ring lead (B-lead) output has a –50 V internal clamp to battery ground (BGND).
C3
0
0
0
0
1
1
1
1
C2
Operating Modes
0
0
1
1
0
0
1
1
The Am79R251 receives multiplexed control data on the P1, P2 and P3 pins. The LD pin then
controls the loading of P1, P2, and P3 values into the proper bits in the Am79R251 control register.
When the LD pin is less than 0.3 V below VREF ( < (VREF – 0.3 V) ), P1–P3 must contain data for
relay control bits RD1, RD2 and RD3. These are latched into the first three bits in the Am79R251
control register. When the LD pin is more than 0.3 V above VREF (> (VREF + 0.3 V) ), P1–P3 must
contain ISLIC control data C1, C2, and C3, which are latched into the last three bits of the Am79R251
control register. Connecting the LD pin to VREF locks the contents of the Am79R251 control register.
The operating mode of the Am79R251 is determined by the C1, C2, and C3 bits in the control register
of the Am79R251. Table 1 defines the Am79R251 operating modes set by these signals.
Under normal operating conditions, the ISLIC device does not have active relays. The Am79R251
to ISLAC device interface is designed to allow continuous real-time control of the relay drivers to
avoid incorrect data loads to the relay bit latches of the Am79R251 devices.
To perform external ringing, the ISLAC device from the Intelligent Access voice family is set to
external ringing mode (RMODE = 1), enables the ring relay, and puts the Am79R251 in the Standby
mode.
C1
0
1
0
1
0
1
0
1
Standby
Tip Open
On-Hook
Transmission,
Fixed Longitudinal
Voltage
Disconnect
Active Boosted
Battery
Active High Battery
Active Low Battery
Active Internal
Ringing
Operating
Mode
1
1
High Battery (BATH)
High Battery (BATH)
and BGND
High Battery (BATH)
and BGND
High Battery (BATH)
and BGND
Low Battery selection
at VBL
High Battery (BATH)
and Positive Battery
(BATP)
and BGND
Low Battery (BATL)
and BGND
High Battery (BATH)
and Positive Battery
(BATP)
Battery Voltage
Selection
Am79R251
(High ohmic feed): Loop
supervision active, A and B
amplifiers shut down
Tip Open: AD at High-Impedance,
Channel A power amplifier shut
down
Fixed longitudinal voltage of –30 V
AD and BD at High-Impedance,
Channel A and B power amplifiers
shut down
Active feed, normal or reverse
polarity
Active internal ringing
Operating Mode
Amplifier Output
Connection
to RMGPi &
Resistors
RMGLi
A and B
Open
Open
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