Am79R251

21

Operating Modes

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.

Table 1.

Operating Modes

Note:

1. In these modes, the ring lead (B-lead) output has a –50 V internal clamp to battery ground (BGND).

C3

C2

C1

Operating

Mode

Battery Voltage

Selection

Operating Mode

Connection

to RMGPi &

RMGLi

Resistors

000

High Battery (BATH)

and BGND

(High ohmic feed): Loop

supervision active, A and B

amplifiers shut down

Open

001

High Battery (BATH)

and BGND

Tip Open: AD at High-Impedance,

Channel A power amplifier shut

down

Open

010

On-Hook

Transmission,

Fixed Longitudinal

Voltage

High Battery (BATH)

and BGND

Fixed longitudinal voltage of –30 V

A and B

Amplifier Output

0

1

1

Disconnect

Low Battery selection

at VBL

AD and BD at High-Impedance,

Channel A and B power amplifiers

shut down

1

0

0

Active Boosted

Battery

High Battery (BATH)

and Positive Battery

(BATP)

Active feed, normal or reverse

polarity

1

0

1

Active High Battery

High Battery (BATH)

and BGND

1

1

0

Active Low Battery

Low Battery (BATL)

and BGND

1

1

1

Active Internal

Ringing

High Battery (BATH)

and Positive Battery

(BATP)

Active internal ringing