
XRT94L33
xr
Rev.1.2.0.
3-CHANNEL DS3/E3/STS-1 TO STS-3/STM-1 MAPPER IC DATA SHEET
198
2.2.6.10
THE IDLE CELL GENERATOR
The Transmit ATM Cell Processor block consists of a “Idle Cell Generator” block.
Figure 28 presents the
functional block diagram of the “Transmit ATM Cell Processor block with the “Idle Cell Generator” block
highlighted.
Figure 28: Illustration of the Transmit ATM Cell Processor block Functional Block Diagram, with the
“Idle Cell Generator” block highlighted
Parity
Checker
Block
Parity
Checker
Block
User Cell
Filter
Block
User Cell
Filter
Block
Cell Extraction
Buffer/
Processor
Cell Extraction
Buffer/
Processor
Cell Insertion
Buffer/
Processor
Cell Insertion
Buffer/
Processor
HEC Byte
Calculation
&
Insertion
Block
HEC Byte
Calculation
&
Insertion
Block
Cell Payload
Scrambler
Block
Cell Payload
Scrambler
Block
TxFIFO
Transmit UTOPIA
Interface Block
Microprocessor
Interface
Block
Microprocessor
Interface
Block
Idle Cell
Generator
Idle Cell
Generator
Main Data Path
To Transmit
SONET/STS-3c
POH
Processor Block
Transmit GFC
Nibble-Field
Input Port
Block
Transmit GFC
Nibble-Field
Input Port
Block
TxGFC
Input Port
Whenever the TxFIFO (within the Transmit UTOPIA Interface block) does not contain a complete cell, the
Transmit ATM Cell Processor will first read out any ATM cell data that resides within the “Transmit Cell
Insertion Buffer” and will insert this (or these) ATM cells into the “Transmit Data Path”.
Once both the
“TxFIFO” and the “Transmit Cell Insertion Buffer” are depleted, then the Transmit ATM Cell Processor block
will automatically fill in the STS-3 SPE bandwidth by generating and transmitting Idle Cells via the “Transmit
Data Path”. By default, the Transmit ATM Cell Processor block will generate Idle Cells that contain header
byte patterns which conform to the ATM Forum recommendations. However, the XRT94L33 does contain
some registers that permit the user to “customize” the header byte and payload byte pattern of these Idle
cells.
The procedure for configuring the Idle Cell Generator to generate and transmit Idle Cells with
“customized” header and payload bytes is presented below.
The Procedure for configuring the Transmit ATM Cell Processor Block to transmit Idle Cells with
“user-specified” header and payload bytes
The user can configure the Transmit ATM Cell Processor block to generate and transmit Idle Cells with “user-
specified” header and payload bytes, by executing the following steps.