
XRT7250
DS3/E3 FRAMER IC
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REV. 1.1.1
196
Hence, a given Terminal Equipment receiving a DS3
data stream can identify the framing format of this
DS3 data stream, by reading the value fo the AIC bit-
field. The Receive DS3 Framer block permits the us-
er’s Microcontroller/MIcroprocessor to determine the
state of the AIC bit-field (within the incoming DS3 da-
ta stream) by writing the value of the AIC bit-field,
within the most recently received DS3 frame, into bit
3 (RxAIC) within the Rx DS3 Status Register (Ad-
dress = 0x11), as illustrated below.
The Receive DS3 Framer block will also generate an
interrupt if it detects a change of state in the AIC bit-
field (within the incoming DS3 data stream). If this
occurs, then the Receive DS3 Framer block will set
Bit 2 (AIC Interrupt Status) within the Rx DS3 Inter-
rupt Stauts Register (Address = 0x13) to “1” as illus-
trated below.r
4.3.2.6
Performance Monitoring of the DS3
Transport Medium
The DS3 Frame consists of some overhead bits that
are used to support performance monitoring of the
DS3 Transmission Link. These bits are the P-Bits
and the CP-Bits.
4.3.2.6.1
P-Bit Checking/Options
The remote Transmit DS3 Framer will compute the
even parity of the payload portion of an outbound
DS3 Frame and will place the resulting parity bit value
in the 2 P-bit-fields within the very next outbound DS3
Frame. The value of these two bits fields is expected
to be the identical.
The Receive DS3 Framer block, while receiving each
of these DS3 Frames (from the remote Transmit DS3
Framer), will compute the even-parity of the payload
portion of the frame. The Receive DS3 Framer block
will then compare this locally computed parity value
to that of the P-bit fields within the very next DS3
Frame. If the Receive DS3 Framer block detects a
parity error, then two things will happen:
1. The Receive DS3 Framer block will inform the P/
C of this occurrence by generating a Detection
of P-Bit Error interrupt,
2. The Receive DS3 Framer block will alter the
value of the FEBE bits, (to a pattern other than
111) that the Near-End Transmit DS3 Framer will
be transmitting back to the remote Terminal.
3. The XRT7250 Framer IC will increment the
PMON Parity Error Event Count Registers
(Address = 0x54 and 0x55) for each detected
parity error, in the incoming DS3 data stream.
The bit-format of these two registers follows.
RXDS3 STATUS REGISTER (ADDRESS = 0X11)
BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0
Reserved
RxFERF
RxAIC
RxFEBE[2:0]
RO
00
000
RXDS3 INTERRUPT STATUS REGISTER (ADDRESS = 0X13)
BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0
CP-Bit Error
Interrupt
Status
LOS
Interrupt
Status
AIS
Interrupt
Status
Idle Interrupt
Status
FERF
Interrupt
Status
AIC
Interrupt
Status
OOF
Interrupt
Status
P-Bit Error
Interrupt
Status
RURRUR
RUR
RURRUR
00
000
100
PMON PARITY ERROR EVENT COUNT REGISTER - MSB (ADDRESS = 0X54)
BIT 7BIT 6BIT 5BIT 4BIT 3BIT2BIT 1BIT 0
Parity Error Count - High Byte
RO
00
000