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ISAC-SX
PEB 3086
Description of Functional Blocks
Data Sheet
135
2003-01-30
For DCL = 1.536 MHz one of the IOM-2 channels 0 - 2 can be selected, for DCL =
4.096 MHz any of the eight IOM-2 channels can be selected.
The channel select pins have direct effect on the timeslot selection of the following
registers:
TR_TSDP_BC1
TR_TSDP_BC2
TR_CR, TRC_CR
DCI_CR, DCIC_CR
MON_CR
HDLC Controllers
The ISAC-SX contains two HDLC controllers. The first one is used for the layer-2
functions of the D- channel protocol (LAPD), the second one provides B-channel access
with reduced FIFO thresholds which can be used for firmware upgrade via the line for
example. By setting the Enable HDLC channel bits (EN_D, EN_B1H) in the DCI_CR/
BCH_CR registers each of the HDLC controllers can access the D or B-channels on
IOM-2.
They perform the framing functions used in HDLC based communication: flag
generation/recognition, bit stuffing, CRC check and address recognition.
The FIFO has a size of 64 byte per direction for the D-channel and 128 byte per direction
for the B-channel. They are implemented as cyclic buffers. The transceiver reads and
writes data sequentially with constant data rate whereas the data transfer between FIFO
and microcontroller uses a block oriented protocol with variable block sizes.
The configuration, control and status bits related to the HDLC controllers are all assigned
to the following address ranges:
Note: For B-channel data access a single address location is used to read from and write
to the FIFO. For D-channel access the address range 00
H
-1F
H
is used (similar as
in ISAC-S PEB 2086), however a single address from this range is sufficient to
access the FIFO as the internal FIFO pointer is incremented automatically
independent from the external address.
The mechanisms for access to the FIFOs are identical for D- and B-channels, therefore
the following description applies to both of them and for simplification specific references
Table 17
HDLC Controller Address Range
FIFO Address
00
H
-1F
H
7A
H
Config/Ctrl/Status Registers
20
H
-29
H
70
H
-79
H
D-channel
B-channel