
á
XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
283
Remote Terminal Equipment), the XRT7250
Framer IC will generate the Completion of Trans-
mission of a LAPD Message Interrupt to the
Microcontroller/Microprocessor. Once the
XRT7250 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.
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.
5.3
THE RECEIVE SECTION OF THE XRT7250 (E3
MODE OPERATION)
When the XRT7250 has been configured to operate
in the E3 Mode, the Receive Section of the XRT7250
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 127 presents a simple illustration of the Re-
ceive Section of the XRT7250 Framer IC.
Each of these functional blocks will be discussed in
detail in this document.
5.3.1
The Receive E3 LIU Interface Block
The purpose of the Receive E3 LIU Interface block is
two-fold:
TXE3 LAPD STATUS AND INTERRUPT REGISTER (ADDRESS = 0X34)
BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0
Not Used
TXDL Start
TXDL Busy
TxLAPD
Interrupt
Enable
TxLAPD
Interrupt
Status
RO
R/W
RO
R/W
RUR
0
0000
001
FIGURE 127. A SIMPLE ILLUSTRATION OF THE RECEIVE SECTION OF THE XRT7250 CONFIGURED TO OPERATE IN
THE
E3 MODE
Receive
Payload Data
Input
Interface Block
Receive DS3/E3
Framer Block
Receive LIU
Interface
Block
RxSer
RxNib[3:0]
RxClk
RxPOS
RxNEG
RxLineClk
Receive Overhead
Input
Interface Block
RxOHClk
RxOHInd
RxOH
RxOHEnable
RxOHFrame
RxFrame
Rx E3 HDLC
Controller/Buffer
Rx E3 HDLC
Controller/Buffer
From Microprocessor
Interface Block