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IDT82P2282
DUAL T1/E1/J1 LONG HAUL / SHORT HAUL TRANSCEIVER
87
August 20, 2009
3.20.2
HDLC TRANSMITTER
The HDLC Transmitter inserts the data into the selected position to
form HDLC packet data stream.
3.20.2.1
HDLC Channel Configuration
In T1/J1 mode ESF & T1 DM formats, three HDLC Transmitters
(#1, #2 & #3) per link are provided for HDLC insertion to the data stream
to be transmitted. In T1/J1 mode SF & SLC-96 formats, two HDLC
Transmitters (#2 & #3) per link are provided for HDLC insertion. In E1
mode, three HDLC Transmitters (#1, #2 & #3) per link are provided for
HDLC insertion. Except in T1/J1 mode ESF & T1 DM formats, the HDLC
channel of HDLC Transmitter #1 is fixed in the DL bit (in ESF format)
and D bit in CH24 (in T1 DM format) respectively (refer to
Table 13 &
Table 14), the other HDLC channel is configured as the follows:
1. Set the EVEN bit and/or the ODD bit to select the even and/or
odd frames;
2. Set the TS[4:0] bits to define the channel/timeslot of the
assigned frame;
3. Set the BITEN[7:0] bits to select the bits of the assigned channel/
timeslot.
Then all the functions of the HDLC Transmitter will be enabled only
if the corresponding TDLEN bit is set to ‘1’.
3.20.2.2
HDLC Mode
Setting the THDLCM bit to ‘0’ (default) in the HDLC Transmitter
selects the HDLC mode (per Q.921).
3.20.2.2.1
HDLC Mode
A FIFO buffer is used to store the HDLC data written in the
DAT[7:0] bits. The FIFO depth is 128 bytes. When it is full, it will be indi-
cated by the FUL bit. When it is empty, it will be indicated by the EMP bit.
If an entire HDLC packet is stored in the FIFO indicated by the
EOM bit, or if the data in the FIFO exceeds the upper threshold set by
the HL[1:0] bits, the data in the FIFO will be transmitted. The opening
flag (‘01111110’) will be prepended before the data automatically. The
transmission will not stop until the entire HDLC data are transmitted.
Then the 2-byte FCS and the closing flag (‘01111110’) will be added to
the end of the HDLC data automatically. During the HDLC data trans-
mission, a zero is stuffed automatically into the serial output data if there
are five consecutive ’One’s ahead.
The abort sequence (‘01111111’) will be inserted to the HDLC
packet anytime when the ABORT bit is set. Or when the FIFO is empty
and the transmitted last byte is not the end of the current HDLC packet,
the abort sequence will be transmitted automatically.
If the TDLEN bit is enabled and there is no HDLC packet in the
FIFO to be transmitted, the 7E (Hex) flag will always be transmitted.
3.20.2.3
Interrupt Summary
In the HDLC mode, when the data in the FIFO is below the lower
threshold set by the LL[1:0] bits, it will be indicated by the RDY bit. When
there is a transition (from ‘0’ to ‘1’) on the RDY bit, the RDYI bit will be
set. In this case, if enabled by the RDYE bit, an interrupt will be reported
by the INT pin.
In the HDLC mode, when the FIFO is empty and the last transmit-
ted byte is not the end of the current HDLC packet, the UDRUNI bit will
be set. In this case, if enabled by the UDRUNE bit, an interrupt will be
reported by the INT pin.
3.20.2.4
Reset
The HDLC Transmitter will be reset when there is a transition from
‘0’ to ‘1’ on the TRST bit. The reset will clear the FIFO.
Bit
Register
Address (Hex)
EVEN
THDLC1 Assignment (E1
only) / THDLC2 Assign-
ment / THDLC3 Assignment
085, 185(E1 only) / 086, 186 / 087,
187
ODD
TS[4:0]
BITEN[7:0]
THDLC1 Bit Select (E1
only) / THDLC2 Bit Select /
THDLC3 Bit Select
088, 188 (E1 only) / 089, 189 /
08A, 18A
TDLEN3
THDLC Enable Control
084, 184
TDLEN2
TDLEN1