Transmit Operation - NEC UPD98413 User Manual

(2) TAG
The µPD98413 supports modes in which a one-word space is inserted in the first word of a cell as a function to
assist the ATM device to append TAG (label) to each cell. In this manual, these modes are referred to as modes
with and without TAG. The TAG mode is set to the MDAPIT and MDAPIR registers.
Transmission
Reception
The user can set any TAG value added to the receive cell in the IADRR register. The µPD98413 sends the
receive cell to ATM interface with the TAG value set to the IADRR register.

4.2.3 Transmit operation

The µPD98413 supports both the direct status indication mode and the status polling mode (Multi-PHY operation
with 1 TXCLAV).
(1) Direct status indication
The µPD98413 implements a dedicated TXCLAV signal for each of the ports. TXCLAV0 corresponds to the
port0, while TXCLAV3 corresponds to the port3.
The ATM device can send a cell to the µPD98413 only when the port has indicated to the ATM device that it is
ready to receive at least one complete cell. The µPD98413 indicates transmit cell buffer available information to
the ATM device. The TXCLAV0-3 are not applicable on the first cycle after TXSOC is asserted, on this cycle, the
µPD98413 keeps the status before the transfer is started. The µPD98413 will deassert TXCLAV unless it can
accept at least one cell (after the currently transferred cell) from the ATM device. Once the TXCLAV0-3 has
been asserted, it will have to stay asserted until the clock edge after assertion of the next TXSOC on that
particular port. The FIFO availability information indicated by TXCLAV is programmable by the FTHT register.
The port to which the next cell will be sent will be selected by TXADDR[1:0] during the clock cycle before
TXENB_B is asserted. This signal will be decoded by the µPD98413 and the specified port will be ready to
receive cell data from the ATM device as soon as the TXENB_B is asserted.
The following figure shows an example of the transmit timing in the direct status indication.
CHAPTER 4 INTERFACES
Table 4-2. Mode of TAG
Mode without TAG (Default)
The word indicated by the high level of
TXSOC is input as the first word of a
cell.
RXSOC is driven high when the first
word of a cell is output.
PRELIMINARY
Mode with TAG
The word in the cycle next to that in
which a word indicated by the high level
of TXSOC is input as the first word of a
cell. The µPD98413 ignores the first
word (TAG).
One word of TAG space is inserted
before the first word of a cell, and
RXSOC is driven high when the TAG
space is output.
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