XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
184
output signal. The clock rate of the TxPOHClk signal
is nominally 768 kHz.
Figure 48 presents a timing diagram depicting the
behavior of the signals associated with the TxPOH
serial input interface during its use.
The TxPOH Serial Input Port also allows the user to
externally insert their POH bytes selectively (e.g.,
some POH bytes are internally generated, others are
externally inserted). This can be accomplished by as-
serting the TxPOHIns and inserting data into the Tx-
POH input at a time when the TxPOH input is expect-
ing this data, per the byte/bit order described above.
If the user wishes to allow the remainder of the data
to be “internally” generated, he/she must negate the
TxPOHIns pin during the time-slot periods for those
POH bytes.
6.3.3.9
The UNI allows the user to disable (or by-pass) the
Transmit PLCP processor and to directly insert the
ATM cells, from the Transmit Cell Processor into the
DS3 payload. The user can exercise this option by
writing to Bit 3 of the UNI Operating Mode Register,
as depicted below.
The “Direct Mapped ATM” Option
The following table presents the relationship between
the value of this bit and the type of ATM Mapping in-
corporated.
F
IGURE
48. A
N
I
LLUSTRATION
OF
THE
B
EHAVIOR
OF
THE
T
X
POH S
ERIAL
I
NTERFACE
SIGNALS
DURING
U
SER
I
NPUT OF
POH D
ATA
.
TxPOHFrame
TxPOH
TxPOHIns
TxPOHClk
t19
t20
t21
t23
t22
t18
UNI Operating Mode Register: Address = 00h
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Local
Loopback
Cell
Loopback
PLCP
Loopback
Reset
Direct
Mapped ATM
C-Bit/M13
TimRefSel[1, 0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
T
ABLE
26: T
HE
R
ELATIONSHIP
BETWEEN
B
IT
3
OF
THE
UNI O
PERATING
M
ODE
R
EGISTER
AND
THE
R
ESULTING
“ATM C
ELL
” M
APPING
M
ODE
.
B
IT
3
M
APPING
M
ODE
0
PLCP Mode:
The PLCP is enabled. PLCP Frames will be mapped into the “outbound” DS3 Frame
1
Direct-Mapped ATM Mode:
The PLCP Processor block is bypassed. ATM cells will be directly mapped into
the “outbound” DS3 Frame