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PRELIMINARY
XRT79L71
542
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
6.3.4.4
RECEIVE SSM CONTROLLER BLOCK INTERRUPTS
Once the Receive SSM Controller block has been enabled, then it can be configured to generate either of the
following two interrupts.
The "Change in SSM Message" Interrupt
The "SSM Out-of-Sequence" Interrupt
The mechanisms causing these interrupts to occur, the procedures for enabling and servicing these two
interrupts is described below.
6.3.4.4.1
THE CHANGE IN SSM MESSAGE INTERRUPT
As mentioned earlier, once the Receive SSM Controller block has been enabled it will begin to receive and
extract out the SSM from the incoming E3 data-stream. Further, we indicated that the Receive SSM Controller
block will continuously write the contents of each incoming SSM into the "RxSSM[3:0]" bit-fields.
In order to alleviate the user from having to use precious "processor overhead" to continuously read out and
poll the contents of the "RxSSM[3:0]" bit-fields, the XRT79L71 includes the "Change in SSM Message"
Interrupt.
Enabling the Change in SSM Message Interrupt
The user can enable the "Change in SSM Message" Interrupt, by executing the following steps.
STEP 1 - Enable the DS3/E3 Framer Block for Interrupt Generation, at the Operational Block Level.
This can be accomplished by setting Bit 2 (DS3/E3 Framer Block Interrupt Enable) within the "Operation
Interrupt Enable Register - Byte 1" to "1" as depicted below.
STEP 2 - Enable the Receive DS3/E3 Framer Block for Interrupt Generation.
This can be accomplished by setting Bit 7 (Receive DS3/E3 Framer Block Interrupt Enable) within the "Framer
Block Interrupt Enable Register" to "1", as depicted below.
Receive E3 SSM Register - G.832 (Address = 0x112C)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RxSSM
Enable
MF[1:0]
Reserved
RxSSM[3:0]
R/W
R/O
1
X
0
X
Operation Interrupt Enable Register - Byte 1 (Address = 0x0116)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
DS3/E3
LIU/JA
Block
Interrupt
Enable
DS3/E3
Framer
Block
Interrupt
Enable
Unused
R/O
R/W
R/O
0
1
0