HDMP-1514 datasheet(3/26 Pages) HP

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658

tions of 10 bit binary words, the

8B/10B code reserves 256 of

them to represent the valid

combinations of 8 bit data. Some

of the remaining combinations

are reserved for special functions.

The character reserved for

defining the transmitted word

boundary has been defined as the

K28.5 character, also known as a

comma character. The receiver

will automatically reset registers

and clock when it receives a

comma character (this will be

discussed in more detail in the

receiver operation section). Every

valid 8 bit data word is actually

represented by one of two 10 bit

codes, indicating either positive

or negative running disparity.

The input latch only generates

the K28.5 character with positive

disparity (0011111010).

In Figure 2, the Frame

Multiplexer utilizes shift registers

and a multi-stage multiplexing

scheme to convert the 10 or 20

parallel data bits to a serial data

stream. This serial data stream is

then fed directly into the Input/

Output Select portion of the

transmitter.

The I/O Select function allows use

of both the internally serialized

Fibre Channel data stream and an

externally supplied Fibre Channel

data stream denoted as

± SI (pins

11 and 12). By using the proper

settings of TS1, TS2, and EWRAP

(pins 76, 75, and 71

respectively), the internal data

stream and the external data

stream can be directed to various

combinations of the cable driver

output, the laser driver output,

and the electrical loopback

output. The possible I/O

combinations are listed in the

Input Output Select Table and the

functionality is described in more

detail in the Transmitter Laser

Driver Operation section below.

The cable driver function

provides a 50

Ω differential cable

driver output at pins 5 and 6

(

± SO). The simplified circuit is

the O-BLL section shown in

Figure 10. A similar output is

provided to allow electrical

loopback, or wrap of the local

data back to the local receiver for

diagnostics. This is denoted as

± LOUT on pin 8 and pin 9.

The final function on the

transmitter chip is the Laser

Driver block which provides a

high speed differential output,

± LZOUT, at pins 19 and 20.

There are several other laser

control I/Os which will be

HDMP-1512 Input Output Select Table

Data Source For:

Active Outputs

Mode

TS1

TS2

EWRAP

± SO

± LZOUT

± LOUT

± SO

± LZOUT ± LOUT

Internal

yes

Internal

yes

Internal

yes

Internal

yes

Internal

yes

Internal

yes

Internal

± SI

yes

Internal

± SI

yes

When operating in the 531.25

Mbaud mode, data byte 0,

Tx[00:09], is active and is

clocked into the input latch a

single byte (10 bits) on each

rising edge of TBC. In the 1062.5

Mbaud mode both data byte 0,

Tx[00:09], and data byte 1,

Tx[10:19], are active. In 1062.5

Mbaud mode, data byte 0 and

data byte 1 are clocked into the

transmitter on the rising edge of

every clock cycle, (TBC). There is

one minor variation possible in

the 1062.5 Mbaud mode, referred

to as “ping-pong” mode. Ping-

pong mode is selected by setting

the PPSEL pin (#34) high. In this

mode the transmitter clocks data

into the input latch one byte per

half clock cycle. Data byte 0 is

transmitted on the rising edge of

TBC and data byte 1 is trans-

mitted 1/2 clock cycle later. See

Figure 16 for timing information.

The input latch will stop sending

the data applied to the Tx[00:09]

data pins when a low is applied to

the -COMGEN pin (#32) and will

send the pre-set special Fibre

Channel character, K28.5 instead.

The 8B/10B coding scheme,

adopted by Fibre Channel, con-

verts 8 bit data words into 10 bit

representations of the actual

data. Of all the possible combina-

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