HFA3841CN Просмотр технического описания (PDF) - Intersil

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HFA3841CN

Wireless LAN Medium Access Controller

Intersil 

HFA3841 System Overview

Preliminary - HFA3841

HOST SYSTEM

(I/O DRIVER)

DISTRIBUTION

SYSTEM

I/O BUS

LAN

FOR STATION ADAPTER

HOST

INTERFACE

MAC

BRIDGE

HFA3841

WIRELESS

MAC

CONTROLLER

FOR ACCESS POINT

PHY

TRANSCEIVER

FIGURE 13. TYPICAL APPLICATION

WIRELESS

MEDIUM

HFA3841

MD0..15

MA1..17

NVCS_

MOE_

MWEL_

MA0/MWEH_

RAMCS_

SPAM

128Kx8

MD0..7

MA1..17

OE_

WE_

CS_

FLASH

128Kx8

MD0..7

MA0..16

CS_

OE_

SRAM

128Kx8

MD8..15

MA1..17

OE_

WE_

CS_

FIGURE 14.

External Memory Interface

An external memory space is provided for firmware and for

buffers that are used for temporary storage of received and

transmitted frames.

The total memory space is 4M bytes. 64K words are used for

control store, where firmware is located. The high data bus

has weak pull-up resistors so that external pull-down resistors

can set the configuration of the HFA3841 during reset.

NVCS- is the enable to the Flash memory device. Typically

the contents of the Flash are copied entirely into SRAM at

initialization, and then rarely if ever accessed during normal

operation. For this reason, it is acceptable to use low cost,

slow Flash devices. During initialization, the clock prescaler

is set to produce a longer cycle time while the Flash is

accessed. Once all the data has been copied, execution

jumps into SRAM and the clock is raised to the normal

operating frequency.

It is possible to operate without a Flash device. In such a

system, the firmware must be downloaded through the host

interface before operation can commence.

The external SRAM memory must be organized in a 16-bit

width to provide adequate performance to implement the

802.11 protocol at 11Mb/s rates. Systems designed for

lower performance applications may be able to use 8-bit

wide memory.

The minimum implementation of external memory consists

of 128K bytes of SRAM organized as 64K x 16. Typical

applications will use 256K bytes organized as 128K x 16. An

access point application could make use of the full address

space of the device with 4M bytes organized as 2M x 16.

16

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