
XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
REV. P1.1.1
262
The bit-format of the Rx DS3 FEAC register is pre-
sented below. It is important to note that the last vali-
dated FEAC code word will be written into the shaded
bit-fields below.
The purpose of generating an interrupt to the μP, up-
on FEAC Code Word Validation is to inform the local
μP that the Framer has a newly received FEAC mes-
sage that needs to be read. The local μP would read-
in this FEAC code word from the Rx DS3 FEAC Reg-
ister (Address = 0x16).
FEAC Code Removal
After the 10th transmission of a given FEAC code
word, the remote terminal equipment may proceed to
transmit a different FEAC code word. When the Re-
ceive FEAC processor detects this occurrence, it
RX DS3 FEAC INTERRUPT ENABLE/STATUS REGISTER (ADDRESS = 0X17)
must Remove the FEAC codeword that is presently
residing in the Rx DS3 FEAC Register. The Receive
FEAC Processor 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 Pro-
cessor will inform the local μP/μC of this removal
event by generating a Rx FEAC Removal interrupt,
and asserting the RxFEAC Remove Interrupt Status
bit in the Rx DS3 Interrupt Enable/Status Register, as
depicted below.
Additionally, the Receive FEAC processor will also
denote the removal event by setting the FEAC Valid
bit-field (Bit 4), within the Rx DS3 FEAC Interrupt En-
able/Status Register to 0, as depicted above.
The description of Bits 0 through 3 within this register,
all support Interrupt Processing, and will therefore be
presented in Section
5.3.6
. Figure 91 presents a flow
diagram depicting how the Receive FEAC Processor
functions.
RX DS3 FEAC INTERRUPT ENABLE/STATUS REGISTER (ADDRESS = 0X17)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
Not Used
Not Used
FEAC
Valid
RxFEAC
Remove
Interrupt
Enable
R/W
X
RxFEAC
Remove
Interrupt
status
RUR
0
RxFEAC
Valid
Interrupt
Enable
R/W
1
RxFEAC
Valid
Interrupt
Status
RUR
1
RO
X
RO
X
RO
X
RO
1
RX DS3 FEAC REGISTER (ADDRESS = 0X16)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
RO
0
RxFEAC [5]
RO
d5
RxFEAC [4]
RO
d4
RxFEAC [3]
RO
d3
RxFEAC [2]
RO
d2
RxFEAC [1]
RO
d1
RxFEAC [0]
RO
d0
Not Used
RO
0
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
Not Used
Not Used
FEAC
Valid
RxFEAC
Remove
Interrupt
Enable
R/W
1
RxFEAC
Remove
Interrupt
status
RUR
1
RxFEAC
Valid
Interrupt
Enable
R/W
X
RxFEAC
Valid
Interrupt
Status
RUR
0
RO
X
RO
X
RO
X
RO
0