Rainbow Electronics DS2151Q - Manual (Page 22)

DS2151Q
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RFDLM1: RECEIVE FDL MATCH REGISTER 1 (Address=29 Hex)
RFDLM2: RECEIVE FDL MATCH REGISTER 2 (Address=2A Hex)
(MSB) (LSB)
RFDL7 RFDL6 RFDL5 RFDL4 RFDL3 RFDL2 RFDL1 RFDL0
SYMBOL POSITION NAME AND DESCRIPTION
RFDL7 RFDL.7 MSB of the FDL Match Code
RFDL0 RFDL.0 LSB of the FDL Match Code
When the byte in the Receive FDL Register matches
either of the two Receive FDL Match Registers
(RFDLM1/RFDLM2), SR2.2 will be set to a one and the
INT2 will go active if enabled via IMR2.2.
6.2 Transmit Section
The transmit section will shift out into the T1 data
stream, either the FDL (in the ESF framing mode) or the
Fs bits (in the D4 framing mode) contained in the Trans-
mit FDL register (TFDL). When a new value is written to
the TFDL, it will be multiplexed serially (LSB first) into
the proper position in the outgoing T1 data stream. After
the full eight bits has been shifted out, the DS2151Q will
signal the host microcontroller that the buffer is empty
and that more data is needed by setting the SR2.3 bit to
a one. The INT2 will also toggle low if enabled via
IMR2.3. The user has 2 ms to update the TFDL with a
new value. If the TFDL is not updated, the old value in
the TFDL will be transmitted once again.
The DS2151Q also contains a zero stuffer which is con-
trolled via the CCR2.4 bit. In both ANSI T1.403 and
TR54016, communications on the FDL follows a subset
of a LAPD protocol. The LAPD protocol states that no
more than 5 ones should be transmitted in a row so that
the data does not resemble an opening or closing flag
(01111110) or an abort signal (11111111). If enabled via
CCR2.4, the DS2151Q will automatically look for 5 ones
in a row. If it finds such a pattern, it will automatically
insert a zero after the five ones. The CCR2.4 bit should
always be set to a one when the DS2151Q is inserting
the FDL. More on how to use the DS2151Q in FDL and
SLC–96 applications is covered in a separate Applica-
tion Note.
TFDL: TRANSMIT FDL REGISTER (Address=7E Hex)
(MSB) (LSB)
TFDL7 TFDL6 TFDL5 TFDL4 TFDL3 TFDL2 TFDL1 TFDL0
SYMBOL POSITION NAME AND DESCRIPTION
TFDL7 TFDL.7 MSB of the FDL code to be transmitted
TFDL0 TFDL.0 LSB of the FDL code to be transmitted
The Transmit FDL Register (TFDL) contains the Facility
Data Link (FDL) information that is to be inserted on a byte basis into the outgoing T1 data stream. The LSB is
transmitted first.