XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
268
7.3.2.7
GFC Nibble Extraction—via the RxGFC
Serial Output Port
The first four bit-field of each cell header are the GFC
bits. The Receive Cell processor will output the con-
tents of the GFC Nibble-field for each cell that it re-
ceives, via the “GFC Nibble Field” serial output port.
The “Receive GFC Nibble-Field” serial output port
consists of the following pins.
RxGFC
RxGFCClk
RxGFCMSB
The data is output via the RxGFC output pin. The or-
der of transmission, within a given cell, is with the
MSB first and in descending order until transmitting
the LSB bit. Afterwards, the “GFC Nibble-field” serial
output port will output the MSB for the GFC Nibble-
field of the next cell. This data is clocked out on the
rising edge of the RxGFCClk output signal. The RxG-
FCMSB output pin will be pulsed “high” each time the
MSB of the GFC Nibble field, for a given cell, is
present at the RxGFC input. Figure 83 presents an il-
lustration depicting the behavior of the RxGFC Serial
Output Port signals.
7.3.2.8
The Receive Cell Processor will generate interrupts
upon
HEC Errors
OAM Cell received
Loss of Cell Delineation
Receive Cell Processor Interrupts
If one of these conditions occur, and if that particular
condition is enabled for interrupt generation, then
when the local μC/μP reads the UNI Interrupt Status
Register, as shown below, it should read ‘xx1xxxxxb’
(where the -b suffix denotes a binary expression, and
‘x’ denotes a “don’t care” value).
At this point, the local μC/μP will have determined that
the Receive Cell Processor block is the source of the
interrupt, and that the Interrupt Service Routine
should branch accordingly. In order to accomplish
this the local μC/μP should now read the “Rx CP Inter-
rupt Status Register” (Address = 4Fh). The bit format
of this register is presented below.
F
IGURE
83. I
LLUSTRATION
OF
THE
B
EHAVIOR
OF
THE
R
X
GFC S
ERIAL
O
UTPUT
P
ORT
SIGNALS
RxGFCClk
RxGFCMSB
t52
RxGFC
BIT 3
BIT 2
BIT 1
BIT 0
t50
t48
t51
t47
t49
UNI Interrupt Status Register (Address = 05h)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
RxDS3
Interrupt
Status
RxPLCP
Interrupt
Status
RxCP
Interrupt
Status
Rx UTOPIA
Interrupt
Status
Tx UTOPIA
Interrupt
Status
TxCP
Interrupt
Status
TxDS3
Interrupt
Status
One Sec
Interrupt
Status
RO
RO
RO
RO
RO
RO
RO
RUR
x
x
1
x
x
x
x
x