XRT74L73 Datasheet, PDF (231/488 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
rupt to the Microcontroller/Microprocessor. Once
the XRT74L73 Framer IC generates this inter-
rupt, it will do the following.
• Assert the Interrupt Output pin (INT) by toggling it
"Low".
• Set Bit 3 (Tx FEAC Interrupt Status) within the Tx
DS3 FEAC Configuration & Status Register, as
illustrated below.
TRANSMIT DS3 FEAC CONFIGURATION & STATUS REGISTER (ADDRESS = 0X31)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Not Used
Tx FEAC
Interrupt
Enable
TxFEAC
Interrupt
Status
TxFEAC
Enable
TxFEAC
GO
TxFEAC
Busy
RO
RO
RO
R/W
RUR
R/W
R/W
RO
0
0
0
1
1
0
0
0
The purpose of this interrupt is to alert the Microcon-
troller/Microprocessor that the Transmit FEAC Pro-
cessor has completed its transmission of a given
FEAC message and is now ready to transmit the next
FEAC Message, to the Remote Terminal Equipment.
4.2.6.1.3 The Completion of Transmission of
the LAPD Message Interrupt
If the Transmit Section interrupts have been enabled
at the Block level, then the Completion of Transmis-
sion of a LAPD Message Interrupt can be enabled or
disabled by writing the appropriate value into Bit 1
(TxLAPD Interrupt Enable) within the Tx DS3 LAPD
Status & Interrupt Register (Address = 0x34), as illus-
trated below.
TXDS3 LAPD STATUS AND INTERRUPT REGISTER (ADDRESS = 0X34)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
Not Used
TxDL Start TxDL Busy
RO
RO
RO
RO
R/W
RO
0
0
0
0
0
0
BIT 1
TxLAPD
Interrupt
Enable
R/W
0
BIT 0
TxLAPD
Interrupt
Status
RUR
0
Setting this bit-field to “1’ enables the Completion of
Transmission of a LAPD Message Interrupt. Con-
versely, setting this bit-field to “0” disables the Com-
pletion of Transmission of a LAPD Message interrupt.
4.2.6.1.4 Servicing the Completion of Trans-
mission of a LAPD Message Interrupt
As mentioned previously, once the user commands
the LAPD Transmitter to begin its transmission of a
LAPD Message, it will do the following.
1. It will parse through the contents of the Transmit
LAPD Message Buffer (located at address loca-
tions 0x86 through 0xDD) and search for a string
of five (5) consecutive “1’s”. If the LAPD Trans-
mitter finds a string of five consecutive “1’s”
(within the content of the LAPD Message Buffer,
then it will insert a “0” immediately after this
string.
2. It will compute the FCS (Frame Check
Sequence) value and append this value to the
back-end of the user-message.
3. It will read out of the content of the user (zero-
stuffed) message and will encapsulate this data
into a LAPD Message frame.
4. Finally, it will begin transmitting the contents of
this LAPD Message frame via the “DL” bits, within
each outbound DS3 frame.
5. Once the LAPD Transmitter has completed its
transmission of this LAPD Message frame (to the
Remote Terminal Equipment), the XRT74L73
Framer IC will generate the Completion of Trans-
mission of a LAPD Message Interrupt to the
Microcontroller/Microprocessor. Once the
XRT74L73 Framer IC generates this interrupt, it
will do the following.
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