am79c972b Advanced Micro Devices, am79c972b Datasheet - Page 23

• Manufacturer Part Number: am79c972b
• Description: Pcnet?-fast+ Enhanced 10/100 Mbps Pci Ethernet Controller With Onnow Support
• Manufacturer: Advanced Micro Devices

General Purpose Serial Interface
CLSN
Collision
CLSN is an input that indicates a collision has occurred
on the network.
Note: The CLSN pin is multiplexed with the COL pin.
RXCLK
Receive Clock
RXCLK is an input. The rising edges of the RXCLK sig-
nal are used to sample the data on the RXDAT input
whenever the RXEN input is HIGH.
Note: The RXCLK pin is multiplexed with the RX_CLK
pin.
RXDAT
Receive Data
RXDAT is an input. The rising edges of the RXCLK sig-
nal are used to sample the data on the RXDAT input
whenever the RXEN input is HIGH.
Note: The RXDAT pin is multiplexed with the RX_ER
pin.
RXEN
Receive Enable
RXEN is an input. When this signal is HIGH, it indicates
to the core logic that the data on the RXDAT input pin
is valid.
Note: The RXEN pin is multiplexed with the CRS pin.
TXCLK
Transmit Clock
TXCLK is an input that provides a clock signal for MAC
activity, both transmit and receive. The rising edges of
the TXCLK can be used to validate TXDAT output data.
Note: The TXCLK pin is multiplexed with the TX_CLK
pin.
TXDAT
Transmit Data
TXDAT is an output that provides the serial bit stream
for transmission, including preamble, SFD, data, and
FCS field, if applicable.
Note: The TXDAT pin is multiplexed with the TXD[0]
pin.
TXEN
Transmit Enable
TXEN is an output that provides an enable signal for
transmission. Data on the TXDAT pin is not valid unless
the TXEN signal is HIGH.
Output
Output
Input
Input
Input
Input
Input
Am79C972
Note: The TXEN pin is multiplexed with the TX_EN
pin.
External Address Detection Interface
EAR
External Address Reject Low
The incoming frame will be checked against the inter-
nally active address detection mechanisms and the re-
sult of this check will be OR’d with the value on the EAR
pin. The EAR pin is defined as REJECT. The pin value
is OR’d with the internal address detection result to de-
termine if the current frame should be accepted or re-
jected.
The EAR pin must not be left unconnected, it should
be tied to VDD through a 10-k
When RST is active, EAR is an input for NAND tree
testing.
SFBD
Start Frame-Byte Delimiter
For the GPSI port during External Address Detec-
tion:
An initial rising edge on the SFBD signal indicates that
a start of frame delimiter has been detected. The serial
bit stream will follow on the SRD signal, commencing
with the destination address field. SFBD will go high for
4 bit times (400 ns when operating at 10 Mbps) after
detecting the second “1” in the SFD (Start of Frame De-
limiter) of a received frame. SFBD will subsequently
toggle every 4 bit times (1.25 MHz frequency when op-
erating at 10 Mbps) with each rising edge indicating the
first bit of each subsequent byte of the received serial
bit stream.
For the External PHY attached to the Media Inde-
pendent Interface during External Address Detec-
tion:
An initial rising edge on the SFBD signal indicates that
a start of valid data is present on the RXD[3:0] pins.
SFBD will go high for one nibble time (400 ns when op-
erating at 10 Mbps and 40 ns when operating at 100
Mbps) one RX_CLK period after RX_DV has been as-
serted and RX_ER is deasserted and the detection of
the SFD (Start of Frame Delimiter) of a received frame.
Data on the RXD[3:0] will be the start of the destination
address field. SFBD will subsequently toggle every nib-
ble time (1.25 MHz frequency when operating at 10
Mbps and 12.5 MHz frequency when operating at 100
Mbps) indicating the first nibble of each subsequent
byte of the received nibble stream. The RX_CLK
should be used in conjunction with the SFBD to latch
the correct data for external address matching. SFBD
will be active only during frame reception.
Note: The SFBD pin is multiplexed with the EESK and
LED1 pins.
5% resistor.
Output
Input
23