XRT74L73 Datasheet, PDF (431/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
mission of a LAPD Message Interrupt to the
Microcontroller/Microprocessor. Once the
XRT74L73 Framer IC generates this interrupt, it
will do the following.
• Assert the Interrupt Output pin (INT) by toggling it
“Low”.
• Set Bit 0 (TxLAPD Interrupt Status) within the TxE3
LAPD Status and Interrupt Register, to “1” as illus-
trated below.
TXE3 LAPD STATUS AND INTERRUPT REGISTER (ADDRESS = 0X34)
BIT 7
RO
0
BIT 6
BIT 5
Not Used
RO
RO
0
0
BIT 4
RO
0
BIT 3
TXDL Start
BIT 2
TXDL Busy
R/W
RO
0
0
BIT 1
TxLAPD
Interrupt
Enable
R/W
0
BIT 0
TxLAPD
Interrupt
Status
RUR
1
The purpose of this interrupt is to alert the Microcon-
troller/MIcroprocessor that the LAPD Transmitter has
completed its transmission of a given LAPD (or PM-
DL) Message, and is now ready to transmit the next
PMDL Message, to the Remote Terminal Equipment.
6.3 THE RECEIVE SECTION OF THE XRT74L73 (E3
MODE OPERATION)
When the XRT74L73 has been configured to operate
in the E3 Mode, the Receive Section of the
XRT74L73 consists of the following functional blocks.
• Receive LIU Interface block
• Receive HDLC Controller block
• Receive E3 Framer block
• Receive Overhead Data Output Interface block
• Receive Payload Data Output Interface block
Figure 192 presents a simple illustration of the Re-
ceive Section of the XRT74L73 Framer IC.
FIGURE 192. THE RECEIVE SECTION OF THE XRT74L73 WHEN IT HAS BEEN CONFIGURED TO OPERATE IN THE E3
MODE
RxOHFrame
RxOHEnable
RxOH
RxOHClk
RxOHInd
RxSer
RxNib[3:0]
RxClk
RxFrame
Receive Overhead
Input
Interface Block
Receive
Payload Data
Input
Interface Block
Receive DS3/E3
Framer Block
Receive LIU
Interface
Block
RxPOS
RxNEG
RxLineClk
From Microprocessor
Interface Block
RRxxEE33HHDDLLCC
CConontrtorolllelre/rB/Buufffefrer
Each of these functional blocks will be discussed in
detail in this document.
6.3.1 The Receive E3 LIU Interface Block
The purpose of the Receive E3 LIU Interface block is
two-fold:
1. To receive encoded digital data from the E3 LIU
IC.
432