AMD
Fig u re 6 -5
Fib e r Op t ic Da t a Lin k De c o u p lin g
As Appropriate
Ferrite Bead (Part# 2743002111 by Fair-Rite)
0.1 µF
4.7 µF
TAXI VCC Plane
As Appropriate
FODL
VCC
Plane
FODL GND Plane
TAXI GND Plane
.1 µF
TAXI GND Plane
4.7 µF
Logic VCC Plane
Power Supply
Ground
Logic GND Plane
4.7 µF
0.1 µF
As Appropriate
12330E-22
Note: This connection includes a ferrite bead in the V
circuit of the fiber optic components.
CC
7 .0 CAS CADE MODE OP ERATION
The TAXIchip set can be cascaded to send multiple byte words over a single serial
channel. Cascade operation is the loading of n bytes of data into a TAXI Transmitter,
and the serial transmission of that data through the Transmitter to the media. Data and
Command bytes are multiplexed into the Local Mode transmitter. Detailed block diagram
and explanation of the data multiplexing method are described in section 7.1. Also see
Appendix C, TAXI TIP #14.
For Am7969-125 TAXI Receivers, the connection is parallel for data and daisy-chained
for control. That is, the SERIN pins of all TAXI receivers are connected together and to
the media. The daisy chain of IGM to CNB control signals determines which Receiver
latches which incoming byte. The Receiver whose CNB input is connected to +5 V is the
primary Receiver, supplying the initial IGM, as well as a reference frequency for the X1
inputs of the down stream TAXI receivers.
Cascade mode does not increase data rate or throughput. The maximum data rate is
100 Mbits per second, cascaded(2) or not. The advantage of cascading lies in the fact
that the width of the data word is transparently maintained. If the application requires the
transfer of 32 bits of data, Cascade mode allows TAXI transmitters to latch all the data,
and send it over a single serial channel, and receive the data in proper order in four
TAXI receivers at the other end of the link.
Another advantage of cascade mode is that if a byte gets corrupted, the system can be
reset by just sending a Sync, ensuring that the first TAXI Receiver gets the first byte, the
second Receiver gets the second byte, and so on. Performing this reset operation with
latches would require additional logic to decode a Sync command which in turn would
reset all the latches.
For Am7969-175 TAXI Receivers, see Appendix C TAXI TIP #13 for single receiver
cascade operation.
(1)Actually, in Non Auto-Repeat Cascade Mode, the throughput is less than 100 Mbits/s due to the need to
send Syncs.
74
TAXIchip Integrated Circuits Technical Manual
AMD [ AMD ]
