AM7968-125JC datasheet(57/127 Pages) AMD

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AMD

TAXIchip Integrated Circuits Technical Manual

Figure 2-1

Basic TAXIchip Operation

6. The Data

comes out the

RX and Data

Strobe is

Raised

Am7968

Transmitter

Am7969

Receiver

1. Parallel Data

is Entered by

the User

2. The Data is

Strobed in by

the User

3. The Data is

Encoded and

then Converted

into a Serial

Stream

4. The Serial

Data is Sent

Out

5. The Re-

ceiver takes the

Serial Data and

Converts it

Back to Parallel

Data and then

Decodes it

Data Out

Data

Strobe

Data In

Strobe

Acknowledge

12330E-3

Three different widths are possible: 8 Data and 4 Command bits, 9 Data and 3 Com-

mand bits, and 10 Data and 2 Command bits. This choice of data and control bus widths

allows flexibility to meet different system bus width requirements, while providing the

capability of merging control and data into a common data stream.

2.2 Operational Modes: Local, Cascade and Test

A TAXIchip set point-to-point link can be operated in one of three modes: Local,

Cascade, or Test. Local mode consists of a single Transmitter communicating with a

single Receiver over the serial medium. Cascade mode for Am7968/7969-125 consists

of a single Transmitter driving two or more daisy chained (cascaded) Receivers over a

single serial medium. Cascade Operation for Am7968/Am7969-175 consists of a single

Transmitter driving a single Receiver as shown in Appendix C, TAXI TIPs #13 and #14.

Cascade mode permits direct interface with 16-bit, 32-bit and wider busses. The link

may be operated in any of the above modes using the TAXl’s internal PLL for bit rate

generation and tracking, or the link may be run in Test Mode with external frequency

multiplying and data tracking PLLs.

3.0 DATA ENCODING, VIOLATION AND SYNCS

3.1 Data Encoding

Any form of serial data transmission requires some form of encoding before the data are

output to the transmission medium. Encoding is the process of converting a set of

data bits to a set of

n code bits.

The purpose of the encoding operation is to include clock information in the data stream.

Without this timing information, the Receiver would not be able to distinguish adjacent

bits of the same value. For example, if we transmit a thousand ONEs followed by a

ZERO, the Receiver might detect only 999 ONEs, or perhaps 1001 ONEs, followed by

one or two ZEROs. An accurate clock is needed to tell the Receiver when to sample the

incoming bit stream to determine if the bit is a ONE or a ZERO. Since the Transmitter

and Receiver have only one data path between them, the clock (timing) information

must be included in the serial data stream.

AM7968-125JC Datasheet(PDF) 57 Page - Advanced Micro Devices

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