CHAPTER 4 INTERFACES
PRELIMINARY
NEC confidential and Proprietary
118
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.
Figure 4-4. Cell Formats
H1
H2
H3
H4
UDF
P1
P2
P3
P4
P5
P6
P7
P8
P45
P46
P47
P48
H5
14 words
32
bits
D0
D31
H1
H2
H3
H4
P1
P2
P3
P4
P5
P6
P7
P8
P45
P46
P47
P48
13 words
D0
D31
H1
H2
H3
H4
UDF
P1
P2
P3
P4
P5
P6
P7
P8
P45
P46
P47
P48
H5
TAG
15 words
D0
D31
H1
H2
H3
H4
P1
P2
P3
P4
P5
P6
P7
P8
P45
P46
P47
P48
TAG
14 words
D0
D31
Type 0
With UDF, 56-byte mode
Type 1
Without UDF, 52-byte mode
Type 3
Without UDF and with TAG
Type 2
With UDF and TAG
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
µ
PD98413 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.
Table 4-1. Mode of UDF
Mode with UDF
Mode without UDF (Default)
Transmission
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.
Cell is input as 52-byte (13-word) data.
The
µ
PD98413 inserts an HEC value
between H4 and P1.
Reception
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.
Received HEC is dropped within the
µ
PD98413 and a cell is output as 52-
byte (13-word) data.
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