HDMP-2634 Avago Technologies US Inc., HDMP-2634 Datasheet - Page 5

• Manufacturer Part Number: HDMP-2634
• Manufacturer: Avago Technologies US Inc.

Specifications of HDMP-2634

• Operating Supply Voltage (typ): 3.3V
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 64
• Lead Free Status / RoHS Status: Not Compliant

SSTL_2 COMPATIBILITY
The HDMP-2634 works with pro-
tocol (FC-1 or MAC) devices
whose VDDQ voltage is nominally
2.5 V. Note that the HDMP-2634
works with a single V
3.3 V. Nonetheless, RX[0:9] and
RBC[0:1] generate output volt-
ages that are compatible with
section 4.1 of the SSTL_2 stan-
dard and are not meant to be
terminated in 50
the HDMP-2634 provides a
VREFR output pin which may be
used at the protocol IC in order
to differentially detect a high or a
low on RX[0:9]. Alternatively,
this voltage may be generated on
the PCB using a resistor divider
from VDDQ or V
the VREFR output of the HDMP-
2634. The HDMP-2634 expects
SSTL_2 compatible signals at the
TX[0:9] and TBC pins. These
pins are unterminated per section
4.1 of the SSTL_2 standard
(Figure 11). The VREFT input
pin is used by the HDMP-2634 to
differentially detect a high or low
on TBC and TX[0:9]. VREFT may
be generated by the protocol
device or on the PCB using a
resistor divider from VDDQ or
V
MULTI-RATE OPERATION
The HDMP-2630/2631 provide
hooks for initializing multi-rate
links. A possible algorithm oper-
ates as follows. In a point to point
link, each node sets its TX_RATE
input pin high to transmit at the
highest possible data rate. At the
same time, each node tries differ-
ent values of RX_RATE to see at
which data rate intelligible data is
received. Once this data rate is
found, TX_RATE is set to enable
this rate. For example, suppose a
5
CC
.
CC
. In addition,
while ignoring
CC
supply of
node that is capable of operating
at 1.25 GBd and 2.5 GBd rates is
establishing a link with a node
that is capable of only 2.5 GBd.
Both nodes will start emitting at
2.5 GBd because this is their
highest rate. The first node will
try receiving at 1.25 GBd rate. It
will not succeed and will there-
fore try 2.5 GBd reception, which
will succeed. The second node is
set to 2.5 GBd and has been re-
ceiving correct data. These two
nodes will settle to 2.5 GBd.
If the second node in the example
above operated at 1.25 GBd only,
then the first node would see
intelligible 1.25 GBd data and set
its TX_RATE=0, at which time
the second node would also start
seeing intelligible data. These
nodes would settle to 1.25 GBd.
If both nodes are 1.25/2.5 GBd
capable, then they will settle to
2.5 GBd. With this algorithm,
nodes need not have a common
lowest common denominator data
rate to interoperate.