CS8900-CQ View Datasheet(PDF) - Cirrus Logic

Part Name

Description

MFG CO.

CS8900-CQ

Highly-Integrated ISA Ethernet Controller

Cirrus Logic 

CS8900

detected. Then the RxEvent register can be read

to determine the final frame status.

The sequence is as follows:

1. At the start of a frame, the byte counter

matches the incoming character counter. The

byte counter will have an even value prior to

the end of the frame.

2. At the end of the frame, the final count, in-

cluding the allowance for the CRC (if the

BufferCRC option is enabled), is held until

the byte counter is read.

3. When a read of the byte counter returns a

count of zero, the previous count was the final

count. The count may now have an odd value.

4. RxEvent should be read to obtain a final status

of the frame, followed by a Skip command to

complete the operation.

Note that all RxEvent’s should be processed be-

fore using the byte counter. The byte counter

should be used following a BufEvent when

RxDest or Rx128 interrupts are enabled.

5.3 Receive Frame Address Filtering

The CS8900 is equipped with a Destination Ad-

dress (DA) filter used to determine which receive

frames will be accepted. (A receive frame is said

to be "accepted" by the CS8900 when the frame

data are placed in either on-chip memory, or in

host memory by DMA). The DA filter can be

configured to accept the following frame types:

Individual Address Frames: For all Individual

Address frames, the first bit of the DA is a "0"

(DA[0] = 0), indicating that the address is a

Physical Address. The address filter accepts Indi-

vidual Address frames whose DA matches the

Individual Address (IA) stored at PacketPage

base + 0158h, or whose hash-filtered DA

matches one of the bits programmed into the

86

Logical Address Filter (the hash filter is de-

scribed later in this section).

Multicast Frames: For Multicast Frames, the

first bit of the DA is a "1" (DA[0] = 1), indicat-

ing that the frame is a Logical Address. The

address filter accepts Multicast frames whose

hash-filtered DA matches one of the bits pro-

grammed into the Logical Address Filter (the

hash filter is described later is this section). As

shown in Table 5.7, Broadcast Frames can be ac-

cepted as Multicast frames under a very specific

set of conditions.

Broadcast Frames: Frames with DA equal to

FFFF FFFF FFFFh. In addition, the CS8900 can

be configured for Promiscuous Mode, in which

case it will accept all receive frames, irrespective

of DA.

Configuring the Destination Address Filter

The DA filter is configured by programming five

DA filter bits in the RxCTL register (Register 5):

IAHashA, PromiscuousA, MulticastA, Individu-

alA, and BroadcastA. Four of these bits are

associated with four status bits in the RxEvent

register (Register 4): IAHash, Hashed, Individu-

alAdr, and Broadcast. The RxEvent register

reports the results of the DA filter for a given

receive frame. The bits associated with DA filter-

ing are summarized below:

Bit #

6

7

9

A

B

RxCTL

Register 5

IAHashA

PromiscuousA

MulticastA

IndividualA

BroadcastA

RxEvent

Register 4

IAHash

(used only if IAHashA = 1)

Hashed

IndividualAdr

(used only if IndividualA = 1)

Broadcast

(used only if BroadcastA = 1)

The IAHashA, MulticastA, IndividualA, and

BroadcastA bits are used independently. As a re-

sult, many DA filter combinations are possible.

DS150PP2

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