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PRELIMINARY
XRT79L71
238
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
Receive DS3 FEAC Interrupt Enable/Status Register (Indirect Address = 0x1117)
The Receive FEAC Controller Block generates an interrupt upon validation and removal of the incoming FEAC
Code words.
4.3.4.1
Operation of the Receive DS3 FEAC Controller Block
The Receive FEAC Controller block will validate or remove FEAC code words that it receives from the remote
Transmit FEAC Controller block. The FEAC Code Validation and Removal functions are described below.
FEAC Code Validation
When the remote Transmit DS3 Framer block wishes to send a FEAC message to the local Receive DS3
Framer block, the remote Transmit DS3 Framer block will transmit this 16 bit message, repeatedly for a total of
10 times. The Receive FEAC Controller block will frame to this incoming FEAC Code Message, and will
attempt to validate this message. Once the Receive FEAC Controller block has received the same FEAC code
word in at least 8 out of the last 10 received codes, it will validate this code word by writing this 6 bit code word
into the Receive DS3 FEAC Register. The Receive FEAC Controller will then inform the P/C of this Receive
FEAC validation event by generating a Rx FEAC Valid interrupt and asserting the FEAC Valid and the Receive
FEAC Valid Interrupt Status Bits in the Receive DS3 Interrupt Enable/Status Register, as depicted below. The
Bit Format of the Receive DS3 FEAC Register is presented below.
The purpose of generating an interrupt to the P/C, upon FEAC Code Word Validation is to inform the P/C
that the Receive FEAC Controller block has a newly received FEAC message that needs to be read. The C/
P should then read-in this FEAC code word from the Receive DS33 FEAC Register (Address = 0x1116).
FEAC Code Removal
After the 10th transmission of a given FEAC code word, the remote Transmit DS3 Framer may start to transmit
a different FEAC code word. When the Receive FEAC Controller detects this occurrence, it must Remove the
FEAC codeword that is presently residing in the Rx DS3 FEAC Register. The Receive FEAC Controller Block
will remove the existing FEAC code word when it detects that 3 or more out of the last 10 received FEAC
codes are different from the latest validated FEAC code word. The Receive FEAC Controller Block will inform
the P/C of this removal event by generating a Rx FEAC Removal interrupt, and asserting the RxFEAC
Remove Interrupt Status bit in the Receive DS3 Interrupt Enable/Status Register, as depicted below.
Receive DS3 FEAC Interrupt Enable/Status Register (Address = 0x1117)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
FEAC Valid
RxFEAC
Remove
Interrupt
Enable
RxFEAC
Remove
Interrupt
Status
RxFEAC
Valid Inter-
rupt Enable
RxFEAC
Valid Inter-
rupt
Status
R/O
R/W
RUR
R/W
RUR
0
1
0
1
Receive DS3 FEAC Register (Address = 0x1116)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
RxFEAC Code[5:0]
Unused
R/O
0
1
0