AM79C874VC AMD (ADVANCED MICRO DEVICES), AM79C874VC Datasheet - Page 12

• Manufacturer Part Number: AM79C874VC
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C874VC

• Lead Free Status / RoHS Status: Not Compliant

This pin becomes the highest-order bit of the receive 5-
bit code group in PCS bypass (PCSBP=HIGH) mode.
This output is ignored in 10BASE-T operation.
TX_ER/TXD[4]
Transmit Error
When TX_ER is asserted, it will cause the 4B/5B en-
coding process to substitute the transmit error code-
group /H/ for the encoded data word.
This pin becomes the higher-order bit of the transmit 5-
bit code group in PCS bypass (PCSBP=HIGH) mode.
This input is ignored in the 10BASE-T operation.
TX_CLK/10TXCLK/PCSBPCLK
Transmit Clock
A free-running clock which provides timing reference
for TX_EN, TX_ER, and TXD[3:0] signals. It is 25 MHz
in 100BASE-TX/FX and 2.5 MHz in 10BASE-T.
When 7-wire GPSI mode is enabled, this pin will pro-
vide a 10 MHz transmit clock for 10BASE-T operation.
When the cable is unplugged, the 10TXCLK ceases
operation.
When working in PCSBP mode, this pin will provide a
25 MHz clock for 100BASE-TX operation, and 20 MHZ
clock for 10BASE-T operation. TX_CLK is high imped-
ance when the ISO pin is enabled.
TX_EN/10TXEN
Transmit Enable
The TX_EN pin is asserted by the MAC to indicate that
data is present on TXD[3:0].
When 7-wire 10BASE-T mode is enabled, this pin is
the transmit enable signal.
TXD[3:1]
Transmit Data
The MAC will source TXD[3:1] to the PHY. The data will
be synchronous with TX_CLK when TX_EN is as-
serted. The PHY will clock in the data based on the ris-
ing edge of TX_CLK.
TXD[0]/10TXD
Transmit Data[0]/10 Mbps Transmit Data
The MAC will source TXD[0] to the PHY. The data will
be synchronous with TX_CLK when TX_EN is as-
serted. The PHY will clock in the data based on the ris-
ing edge TX_CLK.
When 7-wire 10BASE-T mode is enabled, this pin will
transmit serial data.
COL/10COL
Collision
COL is asserted high when a collision is detected on
the media. COL is also used for the SQE test function
in 10BASE-T mode.
10COL is asserted high when a collision is detected
during 7-wire interface mode.
12
Output, High Impedance
Output, High Impedance
Input
Input
Input
Input
D A T A
Am79C874
CRS/10CRS
Carrier Sense
CRS is asserted high when twisted pair media is non-
idle. This signal is used for both 10BASE-T and
100BASE-X. In full duplex mode, CRS responds only
to RX activity. In half duplex mode, CRS responds to
both RX and TX activity.
10CRS is used as the carrier sense output for the
7-wire interface mode.
Miscellaneous Functions
PCSBP
PCS Bypass
The 100BASE-TX PCS as well as scrambler/descram-
bler will be bypassed when PCSBP is pulled high via a
1-4.7 kΩ resistor. TX_ER will become TXD[4] and
RX_ER will become RXD[4].
In 10 Mbps PCS bypass mode, the MII signals are not
valid. The signals that interface to the MAC (i.e.,
DECPC 21143) are located on pins 14 to 19. The sig-
nals are defined as follows:
When left unconnected, the device operates in MII or
GPSI mode.
ISODEF
Isolate Default
This pin is used when multiple PHYs are connected to
a single MAC. When it is pulled high via a 1-4.7 kΩ re-
sistor, the MII interface will be high impedance. The
status of this pin will be latched into MII Register 0, bit
10 after reset.
When this pin is left unconnected, the default condition
of the MII output pins are not in the high impedance
state.
ISO
Isolate
The MII output pins will become high impedance when
ISO is pulled high via a 1-4.7 kΩ resistor. However, the
MII input pins will still respond to data. This allows mul-
tiple PHYs to be attached to the same MII interface.
The same isolate condition can also be achieved by as-
serting MII Register 0, bit 10. In repeater mode, ISO will
not tri-state the CRS pin.
When this pin is left unconnected, the MII output pins
are not in the high impedance state.
S H E E T
— 10RXD± are the differential receive outputs to
— 10TXD± are the differential transmit inputs from
— 10TXD++/10TXD-- are the differential pre-
the MAC.
the MAC.
emphasis transmit outputs from the MAC.
Output, High Impedance
Input, Pull-Down
Input, Pull-Down
Input, Pull-Down
22235K