78Q2120C
10/100BASE-TX
Transceiver
Station Management Interface
78Q2120C. There is an LED pin that indicates the
link is up (LEDL), others that indicate the 78Q2120C
is either transmitting (LEDTX) or receiving (LEDRX),
one that signals a collision event (LEDCOL), two
more that reflect the data rate (LEDBTXand LEDBT),
and one that reflects full duplex mode of operation
(LEDFDX).
The station management interface consists of
circuitry which implements the serial protocol as
described in Clause 22.2.4.5 of IEEE-802.3. A 16-
bit shift register receives serial data applied to the
MDIO pin at the rising-edge of the MDC clock signal.
Once the preamble is received, the station
management control logic looks for the start-of-
frame sequence and a read or write op-code,
followed by the PHYAD and REGAD fields. For a
read operation, the MDIO port becomes enabled as
an output and the register data is loaded into a shift
register for transmission. The 78Q2120C can work
with a one bit preamble rather than the 32 bits
prescribed by IEEE-802.3. This allows for faster
programming of the registers. If a register does not
exist at an address indicated by the REGAD field or
if the PHYAD field does not match the 78Q2120C
PHYAD indicated by the PHYAD pins, a read of the
MDIO port will return all ones. For a write operation,
the data is shifted in and loaded into the appropriate
register after the sixteenth data bit has been
received.
Interrupt Pin
The 78Q2120C has an Interrupt pin (INTR) that is
asserted whenever any of the eight interrupt bits of
MR17.7:0 are set. These interrupt bits can be
disabled via the MR17.15:8 Interrupt Enable bits.
The Interrupt Polarity bit, MR16.14, controls the
active level of the INTR pin. When the INTR pin is
not asserted, this pin is held in a high impedance
state. An external pull-up or pull-down resistor may
be required for use with the INTR pin.
APPLICATIONS REQUIREMENTS
RXIP/N Termination Connection
The input circuitry of the TERIDIAN 78Q2120C has
changed for continuing performance improvements.
Device revision C09 requires that the RXIP/N
termination resistors and transformer center tap
connections be directly connected to VCC for proper
When the PHYAD field is all zeros, the Station
Management Entity (STA) is requesting a broadcast
data transaction.
All PHYs sharing the same
Management Interface must respond to this
broadcast request. The 78Q2120C will respond to
the broadcast data transaction.
receiver operation.
Refer to Figure 1: Typical
Applications Circuit for the schematic showing the
required RXIP/N termination resistors and
transformer center tap connections to VCC for
revision 78Q2120C.
ADDITIONAL FEATURES
LED Indicators
There are seven LED pins that can be used to
indicate various states of operation of the
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© 2009 Teridian Semiconductor Corporation
Rev 1.3
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
