ds2156gn Maxim Integrated Products, Inc., ds2156gn Datasheet - Page 179

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

HEC error correction is disabled, all HEC-errored cells are termed as uncorrectable HEC-errored cells. A
16-bit count of the number of cells that can be written into receive FIFO is maintained, which saturates at
FFFFh. Note that, whether or not ATM layer dequeues cells from the receive FIFO, this counter
increments if valid cells are received. This counter is cleared by the microprocessor interface once it is
latched. A 2k x 8 receive FIFO that holds 4-cell buffer space per port is maintained for rate decoupling.
24.6.2
The DS2156 drives the internal cell-available signals onto the external CLAV lines based on the
configured polling mode. In direct status mode, only four ports are supported. If a port is conducting a
cell transfer, its CLAV is kept asserted until the last byte is transferred to the ATM layer. This supports
interfacing with the octet-level ATM layer also. Cell-available status for any fresh cell corresponding to a
port has to be polled by the ATM layer only after the current cell transfer to the port is completed. The
multiplexed bus with 1CLAV polling mode cycle is depicted in Figure 24-9 in which N, N + 2, N - 3, N -
2, N - 1, N + 3, and N + 1 are considered part of DS2156 UTOPIA ports. During reception of a cell from
PHY N, the other PHYs are polled. It turns out that PHY N - 3 and PHY N + 3 have cells available, and
PHY N + 3 is ultimately selected. (Remember that the PHY number values are for example only). Just
like the transmit interface, the 2-clock polling cycles allow up to 26 PHYs to be polled in the 8-bit mode.
Figure 24-9. Polling Phase and Selection at Receive Interface
CELL RCV FROM:
UR-ADDRx
UR-DATAx
UR-CLAV
UR_ENB
UTOPIA Side Receive: Muxed Mode with One Receive CLAV
UR-CLK
UR-SOC
N+2
1
N+2
P35 P36 P37 P38 P39 P40 P41 P42 P43
1F
2
N-3
3
N-3
1F
4
N-2
5
N-2
1F
POLLING
6
PHY N
N-1
7
N-1
1F
179 of 265
8
N+3
9
N+3
1F
10
N+1
P44
11
N+1
P45 P46 P47 P48
1F
12
N-1
13
SELECTION
N-1
1F
14
N+3
15
N+3
1F
16
N+1
H1
17
POLLING
PHY N+3
N+1
H2
1F
18
N-1
H3
19