ICS1893 datasheet(47/152 Pages) ICST

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Chapter 7

Functional Blocks

ICS1893 Rev C 6/6/00

June, 2000

ICS1893 - Release

7.3.5

PCS Control Signal Generation

For the PCS sublayer, there are two control signals: a Carrier Sense signal (CRS) and a Collision Detect

signal (COL).

The CRS control signals is generated as follows:

When a logic zero is detected in an idle bit stream, the Receive Functions examines the ensuing bits.

When the Receive Functions find the first two non-contiguous zero bits, the Receive state machine

moves into the Carrier Detect state.

As a result, the Boolean Receiving variable is set to TRUE.

Consequently, the Carrier Sense state machine moves into the Carrier Sense ‘on’state, which asserts

the CRS signal.

If the PCS Functions:

a. Cannot confirm either the /I/J/ (IDLE, J) symbols or the /J/K/ symbols, the receive error signal

(RX_ER) is asserted, and the Receive state machine returns to the IDLE state. In IDLE, the

Boolean Receiving variable is set to FALSE, thereby causing the Carrier Sense state machine to

set the CRS signal to FALSE.

b. Can confirm the /I/J/K/ symbols, then the Receive state machine transitions to the ‘Receive’state.

The COL control signal is generated by the transmit modules. For details, see Section 7.3.3.1, “PCS

Transmit Module”.

7.3.6

4B/5B Encoding/Decoding

The 4B/5B encoding methodology maps each 4-bit nibble to a 5-bit symbol (also called a “code group”).

There are 32 five-bit symbols, which include the following:

• Of the 32 five-bit symbols, 16 five-bit symbols are required to represent the 4-bit nibbles.

• The remaining 16 five-bit symbols are available for control functions. The IEEE Standard defines 6

symbols for control, and the remaining 10 symbols of this grouping are invalid. The 6 control symbols

include the following:

– /H/, which represents a Halt, also used to signify a Transmit Error

– /I/, which represents an IDLE

– /J/, which represents the first symbol of the Start-of-Stream Delimiter (SSD)

– /K/, which represents the second symbol of the Start-of-Stream Delimiter (SSD)

– /T/, which represents the first symbol of the End-of-Stream Delimiter (ESD)

– /R/, which represents the second symbol of the End-of-Stream Delimiter (ESD)

If the ICS1893 PCS receives:

– One of the 10 undefined symbols, it sets its QuickPoll Detailed Status Register’s Invalid Symbol bit

(bit 17.7) to logic one.

– A Halt symbol, it sets the Halt Symbol Detected bit in its QuickPoll Detailed Status Register (bit 17.6)

to logic one.

Note:

An STA can force the ICS1893 to transmit symbols that are typically classified as invalid, by both

(1) setting the Extended Control Register’s Transmit Invalid Codes bit (bit 16.2) to logic one and (2)

asserting the associated TXER signal. For more information, see Section 8.11.7, “Invalid Error

Code Test (bit 16.2)”.

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