CS8920A datasheet(89/144 Pages) CIRRUS

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5.2.2

Receive Configuration

After each reset, the CS8920A must be config-

ured for receive operation. This can be done

automatically using an attached EEPROM, or by

wr iting configur ation commands to th e

CS8920A’s internal registers (see Section 3.3).

The items that must be configured include:

• which physical interface to use;

• which types of frames to accept;

• which receive events cause interrupts; and,

• how received frames are transferred.

Configuring the Physical Interface: Configuring

the physical interface consists of determining

which Ethernet interface should be active and

enabling the receive logic for serial reception.

This is done via the LineCTL register (Register

13) and is described in Table 5.1.

Choosing Which Frame Types to Accept: The

RxCTL register (Register 5) is used to determine

which frame types will be accepted by the

CS8920A (a receive frame is said to be "ac-

cepted" when the frame is buffered, either on

chip or in host memory via DMA). Table 5.2 de-

scribes the configuration bits in this register.

Refer to Section 5.3 for a detailed description of

Destination Address filtering.

Selecting Which Events Cause Interrupts: The

RxCFG register (Register 3) and the BufCFG

receive events will cause interrupts to the host

processor. Table 5.3 describes the interrupt en-

able (iE) bits in these registers.

Bit

Bit Name

Operation

SerRxON

When set, reception enabled.

AUIonly

W hen set, AU I s e l e cted (takes

precedence over AutoAUI/10BT).

AutoAUI/

10BT

When set, automatic interface selection

enabled. When both bits 8 and 9 are

clear, 10BASE-T selected.

ELoRx

Squelch

W he n s et , r eceiver squelc h level

reduced by approximately 6 dB.

Table 5.1. Physical Interface Configuration

Bit

Bit Name

Operation

IAHashA

When set, Individual Address frames

that pass the hash filter are accepted*.

7Promis

cuousA

When set, all frames are accepted*.

RxOKA

When set, frames with valid length and

CRC and that pass the DA filter are

accepted.

MulticastA

When set, Multicast frames that pass

the hash filter accepted*.

IndividualA When set, frames with DA that matches

the IA at PacketPage base + 0158h are

accepted*.

BroadcastA When set, all broadcast frames are

accepted*.

CRCerrorA When set, frames with bad CRC that

pass the DA filter are accepted.

RuntA

when set, frames shorter than 64 bytes

that pass the DA filter are accepted.

ExtradataA When set, frames longer than 1518

byt es that pass the DA fil ter are

accepted (only the first 1518 bytes are

buffered).

* Must also meet the criteria programmed into

bits 8, C, D, and E.

Table 5.2. Frame Acceptance Criteria

Bit

Bit Name

Operation

RxOKiE

When set, there is an interrupt if a

frame is received with valid length and

CRC*.

CRCerroriE When set, there is an interrupt if a

frame is received with bad CRC*.

RuntiE

When set, there is an interrupt if a

frame is received that is shorter than

64 bytes*.

ExtradataiE When set, there is an interrupt if a

frame is received that is longer than

1518 bytes*.

* Must also pass the DA filter before there is an

interrupt.

CS8920A

DS238PP2

CS8920A Datasheet(PDF) 89 Page - Cirrus Logic

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