ds2156gn Maxim Integrated Products, Inc., ds2156gn Datasheet - Page 177

• Manufacturer Part Number: ds2156gn
• Description: Ds2156, Ds2156l, Ds2156ln T1/e1/j1 Single-chip Transceiver Tdm/utopia Ii Interface
• Manufacturer: Maxim Integrated Products, Inc.

24.6 Receive Operation
The receive interface of the DS2156 is fully compliant with the ATM Forum’s UTOPIA Level 2
specifications [3]. The DS2156 can be configured to use any address in the range 0 to 31 as its UTOPIA
port addresses. If the receive FIFO is not empty, the cell-available signal is asserted. After cell transfer
from a port, the external cell-available signal updates based on the receive FIFO fill level only after one-
clock cycle from cell-transfer completion. During this one-clock cycle, cell available indication for this
port is kept in the deasserted state. One-clock minimum latency between two cell transfers from the same
UTOPIA port is needed by the DS2156 to update its internal cell pointers.
24.6.1
The received bits, after ignoring framing overhead bits, are checked for possible HEC pattern. The
polynomial used for HEC check is G(X) = 1 + X + X
subtraction (0x55) can be optionally disabled by clearing the register bit U_RCR1.0.
The cell boundaries in the incoming bit stream are identified based on HEC. Figure 24-7 shows the cell-
delineation state machine. The cell-delineation state machine is initially in HUNT state. In HUNT state, it
performs bit-by-bit hunting for correct HEC. If correct HEC is found, it transitions to the PRESYNC state
where it cell-by-cell checks for correct HEC patterns. If DELTA consecutive correct patterns are received
in PRESYNC, the cell-delineation state machine transits to SYNC state. Otherwise, it goes to HUNT
state itself and starts bit-by-bit hunting. In SYNC state, if ALPHA consecutive incorrect HEC patterns are
received, cell delineation is lost and it goes to HUNT state. In PRESYNC and SYNC states, only cell-by-
cell checking for proper HEC pattern is performed. ALPHA and DELTA are 7 and 6, respectively.
Figure 24-7. Cell-Delineation State Diagram
Receive Processing
ALPHA
consecutive
incorrect HEC
Cell by cell
Bit by bit
SYNC
HUNT
177 of 265
Incorrect
HEC
2
DELTA
consecutive
correct HEC
+ X
Correct HEC
8
, as recommended in [4]. The COSET
PRESYNC
Cell
cell
by