MT90520AG ZARLINK [Zarlink Semiconductor Inc], MT90520AG Datasheet - Page 82

• Manufacturer Part Number: MT90520AG
• Description: 8-Port Primary Rate Circuit Emulation AAL1 SAR
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

For ease of programming, it is suggested that consecutive addresses be used. For instance, in a 3-channel VC, the
addresses configured in the Reassembly Circular Buffer Base Address fields should be set to 000h, 001h, and
002h, regardless of the size of the buffers selected. It must be noted that the Reassembly Circular Buffer Base
Address must correspond to the address given within the TDM SDT Reassembly Control Structure (see Figure 13
on page 46) for the chosen TDM channel destination (port- and channel- specific).
Each 16-bit entry in external memory contains a variety of information. Each entry is composed of the fields shown
in Figure 29 and explained in the text below.
•
•
•
•
•
MF - multiframe indicator; this bit is used only when a VC is carrying CAS data (if a VC isn’t carrying CAS,
the MF bits are always zero); the MF bit is set in the buffer for every channel of a VC, each time that the SDT
RX_SAR determines the location of the start of the next multiframe
Res - reserved field; this field always contains a zero
Turn - this field contains a copy of the two most-significant bits of the SDT RX_SAR write pointer for the VC.
These bits represent the “turn” of the circular buffer and are used by the TDM module for underrun detection.
CAS - If CAS data is being processed, this field contains the nibble of data which was last received by this
channel (i.e., in the previous multiframe). CAS data is repeated for an entire multiframe (i.e., 24 consecutive
entries in DS1 case; 16 consecutive entries in E1 case).
TDM Byte - This field contains the TDM data bytes which are extracted from received cells. If dummy cells
have been inserted, this field contains the value of the dummy data programmed by the user.
Table 18 - Formation of SDT Reassembly Circular Buffer Base Addresses to External Memory
Buffer Size
1024 entries
128 entries
256 entries
512 entries
64 entries
MF
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
Figure 29 - Per-Channel SDT Reassembly Circular Buffer
Res
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
{cb_base_add<1:0>,reassembly_circular_buffer_base_add<11:0>,6’b0}
{cb_base_add<0>,reassembly_circular_buffer_base_add<11:0>,7’b0}
{reassembly_circular_buffer_base_add<11:0>,8’b0}
{reassembly_circular_buffer_base_add<10:0>,9’b0}
{reassembly_circular_buffer_base_add<9:0>,10’b0}
Turn
0 1
0 1
0 1
0 1
0 1
0 1
0 1
0 1
0 1
0 1
0 1
0 1
0 1
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
Zarlink Semiconductor Inc.
A B C D
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CAS
MT90520
Address to External Memory
82
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0 0 1 0 1 0 1 0
TDM Byte
Data Sheet