AM79C90 Advanced Micro Devices, AM79C90 Datasheet - Page 36

• Manufacturer Part Number: AM79C90
• Description: CMOS Local Area Network Controller for Ethernet (C-LANCE)
• Manufacturer: Advanced Micro Devices

Serial Transmission
Serial transmission consists of sending an unbroken bit
stream from the TX output pin consisting of:
The Transmission is indicated at the output pin by the
assertion of TENA with the first bit of the preamble and
the negation of TENA after the last transmitted bit.
The C-LANCE starts transmitting the preamble when
the following are satisfied:
36
Preamble/SFD: 56 alternating ONES and ZEROES
terminating with the SFD byte (10101011).
Data: The serialized bit stream from the Transmit
FIFO Shifted out with LSB first.
CRC: The inverted 32-bit polynomial calculated
from the data, address, and type field. CRC is not
transmitted if:
— CLSN becomes asserted any time during
— MODE <03> DTCR = 1 in a normal or loopback
There is at least one byte of data to be transmitted
in the Transmit FIFO.
The interpacket delay has elapsed.
The backoff interval has elapsed, if doing a
retransmission.
— Transmission of the data field is truncated for
AMD
any reason.
transmission.
transmission mode, and ADD_FCS=0 in the
transmit descriptor.
P R E L I M I N A R Y
Am79C90
Serial Reception
Serial reception consists of receiving an unbroken bit
stream on the RX input pin consisting of:
Reception is indicated at the input pin by the assertion of
RENA and the presence of clock on RCLK while TENA
is inactive. The C-LANCE does not sample the received
data until about 800 ns after RENA goes high.
Preamble/SFD: Two ONES occurring a minimum
of 8 bit times after the assertion of RENA.
Destination Address: The 48 bits (6 bytes) follow-
ing the SFD.
Data: The serial bit stream following the Destina-
tion Address. The last 4 complete bytes of data are
the CRC. The Destination Address and the data
are framed into bytes and enter the Receive FIFO.
Source Address and Length field are part of the
data which are transparent to the C-LANCE.