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: 水晶藍的ISA即插即用,即插即用以太網控制器
文件頁數(shù): 108/144頁
文件大小: 1229K
代理商: CDK8920A
5.8
Transmit Operation
5.8.1
Overview
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 trans-
ferred or after the full frame has been transferred
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, us-
ing either Memory or I/O space.
In the second phase of 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 delimiter are
followed by the data transferred into the on-chip
buffer by the host (Destination Address, Source
Address, Length field and LLC data). If the
frame is less than 64 bytes, including CRC, the
CS8920A adds pad bits if configured to do so.
Finally, the CS8920A appends the proper 32-bit
CRC value.
5.8.2
Transmit Configuration
After each reset, the CS8920A must be config-
ured for transmit operation. This can be done
automatically, using an attached EEPROM, or by
writing configuration commands to the
CS8920A’s internal registers (see Section 3.3).
The items that must be configured include which
physical interface to use and which transmit
events cause interrupts.
Configuring the Physical Interface: Configuring
the physical interface consists of determining
which Ethernet interface should be active
(10BASE-T or AUI), and enabling the transmit
logic for serial transmission. Configuring the
Physical Interface is accomplished via the
LineCTL register (Register 13) and is described
in Table 5.12.
Note that the CS8920A will transmit in
10BASE-T mode when no link pulses are being
received only if bit DisableLT is set in register
Test Control (Register 19, bit 7).
Selecting which Events Cause Interrupts: The
TxCFG register (Register 7) and the BufCFG
register (Register B) are used to determine which
transmit events will cause interrupts to the host
processor. Tables 5.13 and 5.14 describe the in-
terrupt enable (iE) bits in these registers.
Register 13, LineCTL
Bit
7
8
Bit Name
SerTxON
AUIonly
Operation
When set, transmission enabled.
When set, AUI selected (takes
precedence over AutoAUI/10BT). When
clear, 10BASE-T is selected.
When set, automatic interface
selection is enabled.
When set, the modified backoff
algorithm is used. When clear, the
standard backoff algorithm is used.
When set, two-part deferral is disabled.
9
AutoAUI/
10BT
Mod
BackoffE
B
D
2-part
DefDis
Table 5.12. Physical Interface Configuration
CS8920A
108
DS238PP2
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