CS8900A
Crystal LAN™ Ethernet Controller
field, pad bits (if necessary), and Frame Check
Sequence (FCS, also called CRC). Figure 9
shows the format of a packet.
Packet R eceived
Pream ble and
Start-of-Fram e
Delim iter Rem oved
5.2.1.2 Frame
The term "frame" refers to the portion of a
packet from the DA to the FCS. This includes
the Destination Address (DA), Source Address
(SA), Length field, Data field, pad bits (if nec-
essary), and Frame Check Sequence (FCS,
also called CRC). Figure 9 shows the format of
a frame. The term "frame data" refers to all the
data from the DA to the FCS that is to be trans-
mitted, or that has been received.
Fram e Pre-
Processed
Fram e
Tem porarily
Buffered
No
Yes
5.2.1.3 Transfer
Use
DMA?
The term "transfer" refers to moving data
across the ISA bus, to and from the CS8900A.
During receive operations, only frame data are
transferred from the CS8900A to the host (the
preamble and SFD are stripped off by the
CS8900A's MAC engine). The FCS may or
may not be transferred, depending on the con-
figuration. All transfers to and from the
CS8900A are counted in bytes, but may be
padded for double word alignment.
Fram e H eld
On Chip
Fram e DM Aed
to Host M em ory
Host R eads
Fram e from
CS8900A M em ory
Host Reads
Fram e from
Host M em ory
Figure 20. Frame Reception
memory via host DMA. This section describes
receive frame pre-processing and Memory
and I/O space receive operation. Section 5.3
on page 90 through Section 5.4 on page 94
describe DMA operation.
5.2.2 Receive Configuration
After each reset, the CS8900A must be config-
ured for receive operation. This can be done
automatically using an attached EEPROM or
by writing configuration commands to the
CS8900A's internal registers (see Section 3.4
on page 21). The items that must be config-
ured include:
5.2.1 Terminology: Packet, Frame, and
Transfer
The terms Packet, Frame, and Transfer are
used extensively in the following sections.
They are defined below for clarity:
•
•
•
which physical interface to use;
which types of frames to accept;
5.2.1.1 Packet
The term "packet" refers to the entire serial
string of bits transmitted over an Ethernet net-
work. This includes the preamble, Start-of-
Frame Delimiter (SFD), Destination Address
(DA), Source Address (SA), Length field, Data
which receive events cause interrupts;
and,
•
how received frames are transferred.
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