Cell Formats - NEC UPD98413 User Manual

4.2.2 Cell Formats

The format of the cell transferred via the ATM interface can be selected from the four types shown in the following
figure.
Type 0
With UDF, 56-byte mode
D31
H1 H5 P1 P5
H2 P2 P6
H3 UDF P3 P7
H4 P4 P8
D0
14 words
Type 1
Without UDF, 52-byte mode
D31
H1 P1 P5
H2
P2 P6
H3
P3 P7
H4 P4 P8
D0
13 words
UDF (User Defined Field): This field is all '00H' at the reception side. It is internally dropped at the transmission side.
TAG: This field is all '00H' at the reception side. It is internally dropped at the transmission side.
(1) UDF
The µPD98413 supports a 52-byte cell format that does not include the H5 byte that is the HEC field of a cell
overhead, and a 56-byte format that includes. If H5 is included, dummy data 'UDF' is also inserted. In this
manual, the 56-byte cell format is referred to as "mode with UDF" and the 52-byte format as "mode without UDF."
The UDF mode is set to the MDAPIT and MDAPIR registers.
Transmission
Reception
118
CHAPTER 4 INTERFACES
Figure 4-4. Cell Formats
P45
32
P46
bits
P47
P48
P45
P46
P47
P48
Table 4-1. Mode of UDF
Mode with UDF
Cell is input as 56-byte (14-word) data.
The internally calculated HEC value is
overwritten to the H5 byte, and UDF is
internally dropped.
Received HEC value and UDF (all '00H')
are combined and inserted into the
second word position of a cell and the
cell is output as 56-byte (14-word) data.
PRELIMINARY
Type 2
With UDF and TAG
D31
H1 H5 P1 P5
H2 P2 P6
TAG
H3 UDF P3 P7
H4 P4 P8
D0
15 words
Type 3
Without UDF and with TAG
D31
H1 P1 P5
H2
P2 P6
TAG
H3
P3 P7
H4 P4 P8
D0
14 words
Mode without UDF (Default)
Cell is input as 52-byte (13-word) data.
The µPD98413 inserts an HEC value
between H4 and P1.
Received HEC is dropped within the
µPD98413 and a cell is output as 52-
byte (13-word) data.
P45
P46
P47
P48
P45
P46
P47
P48
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