MB86960 Datasheet, PDF(16/65 Page) Fujitsu Component Limited. – NETWORK INTERFACE CONTROLLER with ENCODER/DECODER (NICE)

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

MB86960 Datasheet, PDF (16/65 Pages) Fujitsu Component Limited. – NETWORK INTERFACE CONTROLLER with ENCODER/DECODER (NICE)

◁

MB86960

Transmitter Access to Buffer

The size of each of the transmit banks can be changed by

programming the Buffer Size control bits, BS0 and BS1.

The transmit buffer size is thus allocatable by the

software to be a single 2-kilobyte transmit buffer, two

2-kilobyte transmit buffers, two 4-kilobyte transmit

buffers, or two 8 kilobyte transmit buffers. In all

configurations, a single packet or multiple packets can be

loaded into the buffer at one time for transmission. When

a single transmit buffer is used, the system and the

transmitter time-share the use of the buffer. When two

buffers are used, the system can load packets into one of

the buffers while the contents of the other are being

transmitted.

At reset, the pointers are initialized to point to the

beginning of one of the transmit buffers. Each time the

host writes data to the buffer via the Buffer Memory Port

memory location within the transmit buffer. Once a data

byte/word is written, it cannot be read and the internal

pointer cannot be reversed.

Internal pointers managed by NICE control which of the

two banks is selected for access by the host and which

byte/word of the bank is accessed. NICE will switch

banks as soon as the transmit start bit (TX START) of

BMPR10 is written high by the host system. When this

occurs, NICE will start transmitting at the earliest

opportunity. Another automatically-managed pointer,

the transmit-read pointer sequences through the bank

being transmitted to read the packet data into the

transmitter through its FIFO. If a collision occurs, the

packet will be automatically retransmitted after a

pseudo-random waiting interval called the backoff

interval. If there are multiple packets in the bank, NICE

will continue down the list, automatically transmitting

them all. The details of this operation are described in the

section on packet transmission.

NICE has the capability to transmit multiple back-to-

back packets of varying legal Ethernet sizes to the LAN

network. These packets may vary in length from 60 bytes

to 1,514 bytes, excluding preamble and CRC fields. As

shown in Figure 8, multiple packets can reside within one

transmit bank, separated by a non-transmitted, two-byte

header which provides the length of the packet in bytes.

Upon reaching the end of the âlistâ or âchainâ of packets,

the transmitter will stop, update itâs status bits and, if

enabled, generate an interrupt.

Transmit Packet Data Formats

The packets to be transmitted, less preamble and CRC

fields, are first loaded into the transmit buffer along with

a two-byte header indicating the packet length in bytes.

See Figure 8 for details. Multiple packets can be loaded at

the same time provided there is room in the buffer. After

the packets are loaded, the host initiates transmission by

writing the number of packets just loaded into a register

for this purpose on the chip. If the two-bank buffer

configuration has been selected, the second bank can

now be loaded with additional packets.

LENGTH LSB

LENGTH MSB

DATA 1

LENGTH LSB

LENGTH MSB

DATA 2

LENGTH LSB

LENGTH MSB

DATA 3

LENGTH LSB

LENGTH MSB

DATA 4

DATA n

UNUSED BUFFER

AREA

PACKET 1

PACKET 2

Figure 8. Transmit Buffer Detail

▷