PMC-Sierra, Inc.
PRELIMINARY
PM5381 S/UNI-2488
DATASHEET
PMC-2000489
ISSUE 1
SATURN USER NETWORK INTERFACE FOR 2488 MBIT/S
The Transmit UTOPIA Level 3 System Interface Timing diagram (Figure 23) illustrates the
operation of the system side transmit UL3 interface. The single PHY case shown Figure 23
illustrates the behaviour of the TCA signal. At the start of cycle 4, there is only enough FIFO
buffer space for the cell being transferred so TCA is deasserted. The deassertion occurs on the
TFCLK edge after TSOC of the cell (cell#1) being written to the FIFO is sampled. This cell will
take the last remaining cell buffer space in the FIFO. This TCA behaviour is consistent with the
Utopia L3 specification which states that TCA is invalid on the TFCLK edge that initiates the
transition of TSOC to logic 1.
On cycle 5, a cell has been read out of the FIFO to the S/UNI-2488 core so it now has room to
accomodate the cell currently being transferred (cell#1) plus one additional cell (cell#2). At the
start of cycle 8, the transfer of cell#1 is completed. TCA remains high because there is still buffer
space for one more cell. At the start of cycle 10, transfer of cell#2 starts. TCA is deasserted at
cycle 11 because besides the space for holding cell#2, there is no FIFO space for any more cells.
Note that the single-PHY mode is handled exactly like the multi-PHY mode except that the PHY
address is held at the value 0. However, TENB must be set to logic 1 between cell transfers as
shown in Figure 23. Back-to-back cell transfers is not allowed.
TSOC must be high during the first byte of the ATM cell structure and must be present for the
start of each cell. Thus, TSOC will mark the H1 byte. If TSOC is asserted at the wrong time (not
at proper cell boundaries), a corrupted (but complete) cell will be transmitted from the S/UNI-
2488. This corrupted cell will contain the bytes from the runt cell transferred through the UL3
interface plus some random bytes to fill the remainder of the ATM cell.
Figure 23 Single-PHY Utopia Level 3 Transmit Functional Timing
1
2
3
4
5
6
7
8
9
10
11
12
TFCLK
TCA
TENB
TSOC
TDAT[31:0]
TPRTY
H1
P1
P2
P3
P12
H1
P1
P2
P3
Proprietary and Confidentail to PMC-Sierra Inc., and for its Customer’s Internal Use
442
PMC [ PMC-SIERRA, INC ]
