
XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
PRELIMINARY
122
The role of the registers for Idle Cell Pattern—Bytes 1
through 4 is quite straightforward. When the Transmit
Cell Processor opts to generate an Idle cell, it will
read in the content of these registers and send these
values onto the HEC Byte Calculator. Consequently,
the contents of the “Transmit Idle Cell Pattern—Head-
er Byte 5” will likely be overwritten by the HEC Byte
Calculator in the Idle Cell, unless the HEC Byte Cal-
culator has been disabled (See Section 6.2.2.1.2). The
payload portion of these Idle Cells is defined by the
contents of the Transmit Idle Cell Payload Register
(Address = 69h), repeated 48 times. When the Transmit
Cell Processor reads in this register to form the cell
payload, the resulting payload will be sent on to the
Cell Scrambler and is (optionally) scrambled just like
any assigned cell.
The UNI will keep track of the number of Idle cells that
have been generated and transmitted to the Transmit
PLCP Processor (or the Transmit DS3 Framer). The
Transmit Cell Processor increments the contents of
the “PMON Transmitted Idle Cell Count (MSB and
LSB)” Registers (Address = 38h and 39h) for each
Idle Cell that is generated and transmitted. These two
registers are “Reset-upon-Read” registers that, when
concatenated, presents a 16-bit representation of the
total number of idle cells generated and transmitted
since the last time these registers were read. The bit
format of these two registers follow.
T
ABLE
10: B
IT
F
ORMAT
OF
THE
T
X
CP I
DLE
C
ELL
P
ATTERN
-H
EADER
B
YTES
AND
T
X
CP C
ELL
P
AYLOAD
R
EGISTERS
R
EGISTER
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
TxCP Idle Cell Pattern—Header Byte 1
Transmit Idle Cell Pattern—Header Byte 1
TxCP Idle Cell Pattern—Header Byte 2
Transmit Idle Cell Pattern—Header Byte 2
TxCP Idle Cell Pattern—Header Byte 3
Transmit Idle Cell Pattern—Header Byte 3
TxCP Idle Cell Pattern—Header Byte 4
Transmit Idle Cell Pattern—Header Byte 4
TxCP Idle Cell Pattern—Header Byte 5
Transmit Idle Cell Pattern—Header Byte 5
TxCP Idle Cell Payload
Transmit Idle Cell Payload
T
ABLE
11: A
DDRESS
AND
D
EFAULT
V
ALUES
OF
THE
T
X
CP I
DLE
C
ELL
P
ATTERN
R
EGISTERS
A
DDRESS
R
EGISTER
D
EFAULT
V
ALUE
64h
TxCP Idle Cell Pattern—Header Byte 1
00h
65h
TxCP Idle Cell Pattern—Header Byte 2
00h
66h
TxCP Idle Cell Pattern—Header Byte 3
00h
67h
TxCP Idle Cell Pattern—Header Byte 4
01h
68h
TxCP Idle Cell Pattern—Header Byte 5
52h
69h
TxCP Idle Cell Payload
5Ah
PMON Transmitted Idle Cell Count—MSB (Address = 38h)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Tx Idle Cell Count—High Byte
RO
RO
RO
RO
RO
RO
RO
RO
0
0
0
0
0
0
0
0