
MT90503
Data Sheet
69
Zarlink Semiconductor Inc.
4.3.6 Miscellaneous TX_SAR Features
4.3.6.1 T1 with CAS and E1 with CAS Cell Format Mapping
For the transmission of T1 with CAS and E1 with CAS, the number of frames required is 9000 and 6000
respectively. But, because the number of frames mapped in a full size transmit event scheduler is always a
multiple of eight, the MT90503 handles large size schedulers by dividing the size by eight, and mapping eight
times less events (1125 for T1 with CAS and 750 for E1 with CAS). This results in a latency of one frame.
Current Entry
Current Entry
+E/b15:b4
The Current Entry field tells the SAR what the first channel is
to be assembled in this cell. The valid values for this field are
contained between the First Entry
and the Last Entry fields
inclusively. The Current Entry field
also points to words, and is
initialised by software to the word pointed to by the First Entry
field. the The Current Entry field is similar the Last Entry field,
such that it is defined as the offset between the Current Entry
field and the 8 kB boundary in which the structure is contained.
I
Structure
Initialised Bit
+E/b3
The I bit is set by the hardware when a scheduler entry flagged
with the Start bit asserted high is encountered, i.e., as soon as
the first cell is sent on this VC.
This bit is cleared by the software upon initialisation.
Seq
AAL1
Sequence
Number
+E/b3:b0
These bits are reset by software.
tx_sar_read_
pnt
Tx_sar_read
_pnt
+10/b15:b6
This value is a pointer to the next byte to be read in the TX/RX
Circular Buffers.
Transmitted
Cell Counter
Free running
transmitted
cell counter
+12,
+14/b15:b0
The Transmitted Cell Counter increments each time a cell is
transmitted on the VC.
The time needed for the counter to wrap-around decreases
proportionately with the number of channels in the VC.
This field should be reset by software and is used for
monitoring.
V
TDM
Channel
Valid
+16 to
end/b15
When this bit is high the channel is active. When this bit is ’0’,
the programmable null byte, found in register 0420h, will be
transmitted.
Channel N's
TX/RX
Circular
Buffer
Pointer
Channel N's
TX/RX
Circular
Buffer
Pointer
+16 to
end/b13:b0
This field is a pointer to the TX/RX Circular Buffer associated
with this channel. "0000 0000" will be appended to this field as
the LSBs to form a 22-bit address in data memory.
Field
Name of
Field
Byte
Address
Offset /Bits
Used
Description of Field
Table 22 - Description of the Fields for the TX_SAR Control Structure (continued)