
MT90520
Data Sheet
63
Zarlink Semiconductor Inc.
.
Figure 24 - Overview of CBR Data Segmentation Process (SDT Mode)
4.5.4 Data TX_SAR Module
The TX_SAR (and specifically the sub-module which shall henceforth be called the Data TX_SAR) is capable of
transmitting non-CBR data cells which are not associated with any TDM port. These cells may be AAL5 signalling
cells, OAM-type data cells, or any other ATM cells which need to be transmitted from a system containing an
MT90520 device.
The Data TX_SAR does not process or manipulate the data cells. Rather, it simply reads cells which have been
written to a multi-cell circular buffer in external memory by a CPU. It then transfers those cells to the UTOPIA
module for transmission onto the UTOPIA bus.
The Data TX_SAR can operate simultaneously with the generation of AAL1 CBR cells by the TX_SAR.
4.5.4.1 Mode of Operation
The Data TX_SAR within the MT90520 must be enabled, by setting the
Data TX_SAR Enable
bit in the Data
TX_SAR Control Register at address 103Eh.
The user writes the cells to a buffer located in external memory. The address and size of this buffer are
programmed in the DTCON register, located at address 1038h. The cell structure format is illustrated in Figure 25.
When the Data TX_SAR is enabled, it begins to send cells from the cell buffer beginning with the cell pointed to by
the Data TX_SAR Read Pointer. The Read Pointer is incremented after each cell is sent. Cell transmission halts
when the Read Pointer is equal to the user-defined Data TX_SAR Write Pointer, which indicates the cell structure
number being written to by the CPU. Cell transmission begins again after the Write Pointer is changed to a different
value than the Read Pointer. The cell buffer is circular; the Read Pointer will never point above the top of the buffer.
TDM
Input
Buffer
DSTi
CSTi
STiCLK
STiMF
TDM Interface
Module (one per
port)
TX_SAR
UTO_OUT_CLK
UTO_OUT_ENBATM_CLAVPHY
UTO_OUT_CLAVATM_ENBPHY
UTO_OUT_SOC
UTO_OUT_DATA[15:0]
UTO_OUT_PAR
TX
UTOPIA
FIFO
UTOPIA Module
SDT Segmentation
Control Structure
(one per VC in
internal memory)
MT90520
External
ZBT
SRAM
SDT Segmentation
Circular Buffers (one
per TDM channel)