AM7968-125JC datasheet(78/127 Pages) AMD

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AMD

TAXIchip Integrated Circuits Technical Manual

Figure 6-5

Fiber Optic Data Link Decoupling

Note: This connection includes a ferrite bead in the VCC circuit of the fiber optic components.

FODL GND Plane

TAXI VCC Plane

Ferrite Bead (Part# 2743002111 by Fair-Rite)

0.1

µF

4.7

µF

4.7

µF

FODL

VCC

Plane

As Appropriate

Logic VCC Plane

Power Supply

Ground

12330E-22

Logic GND Plane

As Appropriate

TAXI GND Plane

µF

4.7

µF

0.1

µF

TAXI GND Plane

7.0 CASCADE MODE OPERATION

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.

AM7968-125JC Datasheet(PDF) 78 Page - Advanced Micro Devices

AM7968-125JC Datasheet(HTML) 78 Page - Advanced Micro Devices

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