AM79D2251VC datasheet(7/35 Pages) AMD

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Am79D2251

PIN DESCRIPTIONS

Pin Name

I/O

Description

AGND1,

AGND2

Analog Ground

Analog circuitry ground returns

DCLK/S0

Data Clock/GCI

Address Strap 0

Provides data control for MPI interface control. For GCI operation, this pin is device address

bit 0. 5 V tolerant.

DGND1–

DGND2

Digital Ground

Digital ground returns

DIO/S1

Data I/O/GCI Address

Strap 1

I/O

For PCM backplane operation, control data is serially written into and read out of the ISLAC

device via the DIO pin with the MSB first. The data clock (DCLK) determines the data rate.

DIO is high impedance except when data is being transmitted from the ISLAC device under

control of CS/RST. For GCI operation, this pin is device address bit 1. 5 V tolerant.

DRA/DD

RX Path A Backplane

Data/ GCI data

Downstream, Receive

Path B backplane data

For the PCM highway, the receive PCM data is input serially through the DRA ports. The

data input is received every 125 µs and is shifted in, MSB first, in 8-bit PCM or 16-bit linear

bursts at the PCLK rate. The receive port can receive information for direct control of the

ISLIC device. This mode is selected in Device Configuration Register 2 (RTSEN = 1,

RTSMD = 1). When selected, this data is received in an independently programmable

timeslot from the PCM data. For the GCI mode, downstream receive and control data is

accepted on this pin. 5 V tolerant.

DXA/DU

TX Path A Backplane

Data/GCI Data

Upstream, TX Path B

Backplane Data

For the PCM highway, the transmit PCM data is transmitted serially through the DXA port.

The transmission data output is available every 125 µs and is shifted out, MSB first, in 8-bit

PCM or 16-bit linear bursts at the PCLK rate. DXA is high impedance between bursts and

while the device is in the inactive mode. Can also select a mode (RTSEN = 1, RTSMD = 1

or 0 in Device Configuration Register 2) that transmits the Signaling Register MSB contents

first, in an independently programmable timeslot from the PCM data. This data is transmitted

in all modes except disconnect. For the GCI mode, upstream transmit and signaling data is

transferred on this pin. 5 V tolerant.

FS/DCL

Frame sync/GCI

Downstream Clock

For PCM operation, pin is Frame Sync. PCM operation is selected by the presence of an

8 kHz Frame Sync signal on this pin in conjunction with the PCLK on the PCLK/FS pin

(see below). This 8 kHz pulse identifies the beginning of a frame. The ISLAC device

references individual timeslots with respect to this input, which must be synchronized to

PCLK. GCI operation is selected by the presence of the downstream clock DCL, on this

pin in conjunction with the presence of a FS on the PCLK/FS pin. In GCI mode, the rate

at which data is shifted into or out of the PCM ports is a derivative of this DCL clock as

selected in Device Configuration Register 1. 5 V tolerant.

INT/S2

Interrupt/GCI Address

Strap 2

For PCM operation, when a subscriber line requires service, this pin goes to a logic 0 to

interrupt a higher level processor. Several registers work together to control operation of

the interrupt: Signaling and Global Interrupt Registers with their associated Mask

Registers, and the Interrupt Register. See the description at configuration register 6 (Mask)

for operation. Logic drive is selectable between open drain and TTL-compatible outputs.

The S2 function is only available on the dual ISLAC device. For GCI operation, it is the

device address bit 2.

IREF

Current Reference

External resistor (RREF) connected between this pin and analog ground generates an

accurate, on-chip reference current for the A/D's and D/A's on the ISLAC chip.

LD1–LD2

The LD pins output 3-level voltages. When LDn is a logic 0, the destination of the code on

P1–P3 is the relay control latches in the ISLIC control register. When LDn is a logic 1, the

destination of P1–P3 is the mode control latches. LDn is driven to VREF when the contents

of the ISLIC control register must not change.

MCLK

Master Clock

For PCM backplane operation, a DSP master clock connects here. A signal is required

only for PCM backplane operation when PCLK is not used as the master clock. MCLK can

be a wide variety of frequencies. Upon initialization the MCLK input is disabled, and relevant

circuitry is driven by a connection to PCLK. The MCLK connection may be re-established

under user control. 5 V tolerant.

PCLK/FS

PCM Clock/Frame

Sync

For PCM operation, this is PCM Clock. PCM operation is selected by the presence of a

PCLK signal on this pin in conjunction with the FS on the FS/DCL pin (see below). For

PCM backplane operation, connect a data clock, which determines the rate at which PCM

data is serially shifted into or out of the PCM ports. PCLK can be any multiple of the FS

frequency. The minimum clock frequency for linear/ companded data plus signaling data

is 256 kHz. For GCI operation, this pin is Frame Sync. The FS signal is an 8 kHz pulse

that identifies the beginning of a frame. The ISLAC device references individual timeslots

with respect to this input, which must be synchronized to DCL. 5 V tolerant.

P1–P3

ISLIC Control

Control the operating modes of the two ISLIC devices connected to the dual ISLAC device.

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