NEC UPD98413 User Manual page 124

The µPD98413 supports back-to-back transfer of cells. In the case of back-to-back transfer the ATM device
implicitly reselects the µPD98413 port and RXENB_B asserted during the next to the last cycle of the cell transfer.
The second cell is transferred immediately after the previous one and the RXSOC is asserted to indicate the start
of cell. This example is illustrated below.
Figure 4-10. Back-to-back Cell Reception (Direct Status Indication)
RXCLK
RXADDR[1:0]
X PORT0
RXCLAV0
RXCLAV1
RXCLAV2
RXCLAV3
RXENB_B
RXDATA[31:0] P10 P11
RXPRTY
RXSOC
X : Invalid
(2) Status polling (Multi-PHY operation with 1 RXCLAV)
In the status-polling mode, the ATM device can receive the µPD98413 port FIFO status information through the
polling mechanism. In this mode, only RXCLAV0 is used. RXCLAV1-3 are not used, and these signals are fixed
to low.
The ATM device controls the flow of data from the µPD98413 on a per cell basis. The ATM device can explicitly
select the µPD98413 port for transfer of a cell only when the port has indicated to the ATM device that it has at
least one cell available, using the RXCLAV0.
The ATM device polls by presenting the port address on RXADDR[1:0]. The µPD98413 responds two clock
cycles later by driving RXCLAV0 high if the port is ready to send one or more complete ATM cells to the ATM
device; RXCLAV0 is driven low otherwise. Once the RXCLAV0 response for a particular port indicates cell
availability, responses to subsequent polls of that port continues to indicate cell availability until the RXSOC is
asserted for that port.
RXADDR[1:0] during the clock cycle before asserting the RXENB_B signal will select the port which will transfer
the next cell across the ATM interface. The µPD98413 will decode this signal and the specified port will be ready
to transfer cell data two clock cycles before the end of the cell transfer, unless a back-to-back transfer is intended.
The decode-response timing between the RXENB_B and the RXDATA[31:0] is therefore two clock cycles
The following figure shows an example of the transmit timing in the status polling.
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CHAPTER 4 INTERFACES
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P12 X H1 P8
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PRELIMINARY
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P9 P10 P11 P12 H1
NEC confidential and Proprietary
P1 P2 P3 P4
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