參數(shù)資料
型號: CDK8920A
廠商: Cirrus Logic, Inc.
英文描述: CRYSTAL LAN ISA PLUG-AND-PLAY ETHERNET CONTROLLER
中文描述: 水晶藍(lán)的ISA即插即用,即插即用以太網(wǎng)控制器
文件頁數(shù): 14/144頁
文件大?。?/td> 1229K
代理商: CDK8920A
3.0
FUNCTIONAL DESCRIPTION
3.1
Overview
During normal operation, the CS8920A performs
two basic functions: Ethernet packet transmis-
sion and reception. Before transmission or
reception is possible, the CS8920A must be con-
figured.
Configuration
The CS8920A must be configured for packet
transmission and reception at power-up or reset.
Various parameters must be written into its inter-
nal Configuration and Control registers such as
Memory Base Address; Ethernet Physical Ad-
dress; what frame types to receive; and which
media interface to use. Configuration data can
either be written to the CS8920A by the host
(across the ISA bus), or loaded automatically
from an external EEPROM. Operation can begin
after configuration is complete.
Sections 3.1 and 3.3 describe the configuration
process in detail. Section 4.4 provides a detailed
description of the bits in the Configuration and
Control Registers.
Packet Transmission
Packet transmission occurs in two phases. In the
first phase, the host moves the Ethernet frame
into the CS8920A’s buffer memory. The first
phase begins with the host issuing a Transmit
Command. This informs the CS8920A that a
frame is to be transmitted and tells the chip
when (i.e. after 5, 381, or 1021 bytes have been
transferred or after the full frame has been trans-
ferred to the CS8920A) and how the frame
should be sent (i.e. with or without CRC, with or
without pad bits, etc.). The host follows the
Transmit Command with the Transmit Length,
indicating how much buffer space is required.
When buffer space is available, the host writes
the Ethernet frame into the CS8920A’s internal
memory, either as a Memory or I/O space opera-
tion.
In the second phase of packet transmission, the
CS8920A converts the frame into an Ethernet
packet, then transmits it onto the network. The
second phase begins with the CS8920A transmit-
ting the preamble and Start-of-Frame delimiter
as soon as the proper number of bytes have been
transferred into its transmit buffer (5, 381, 1021
bytes or full frame, depending on configuration).
The preamble and Start-of-Frame are followed
by the Destination Address, Source Address,
Length field and LLC data (all supplied by the
host). If the frame is less than 64 bytes, includ-
ing CRC, the CS8920A adds pad bits if
configured to do so. Finally, the CS8920A ap-
pends the proper 32-bit CRC value.
Section 5.8 provides a detailed description of
packet transmission.
Packet Reception
Like packet transmission, packet reception oc-
curs in two phases. In the first phase, the
CS8920A receives an Ethernet packet and stores
it in on-chip memory. The first phase begins
with the receive frame passing through the ana-
log front end and Manchester decoder where
Manchester data is converted to NRZ data. Next,
the preamble and Start-of-Frame delimiter are
stripped off and the receive frame is sent through
the address filter. If the frame’s Destination Ad-
dress matches the criteria programmed into the
address filter, the packet is stored in the
CS8920A’s internal memory. The CS8920A then
checks the CRC, and depending on the configu-
ration, informs the processor that a frame has
been received.
In the second phase, the host transfers the re-
ceive frame across the ISA bus and into host
memory. Receive frames can be transferred as
Memory space operations, I/O space operations,
or as DMA operations using host DMA. In addi-
CS8920A
14
DS238PP2
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