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available (RPXA) signals. The receive bus is used to transfer cell data whenever one of the ports is selected for cell
data transfer. RSOX is asserted during the first transfer of a cell, cell data is transferred on RDATA, and the data
bus parity is indicated on RPRTY. All signals are sampled or updated using RSCLK. The data bus is tri-stated
unless
REN is asserted (low) and one of the ports is selected for data transfer. The RDXA and RPXA signals are
used to indicate when the Receive FIFO has a programmable number of cells available for transfer. There is an
RDXA for each port in the device. RDXA goes high when the associated port's Receive FIFO contains more than a
programmable number of cells. RDXA goes low when the associated port's Receive FIFO is empty (does not
contain any cells). RPXA reflects the current status of a port's RDXA signal when the port is polled. The RPXA
signal is tri-stated unless one of the ports is being polled for FIFO fill status.
10.6.6.2 UTOPIA Level 3, Receive Side
In UTOPIA Level 3, the ATM layer device pulls cells across the system interface. The ATM layer device polls the
individual ports to determine which ports have cells available, and selects a port for cell transfer. Only one PHY
layer device can be present on a UTOPIA Level 3 bus. Whether or not the HEC byte is transferred with the cells is
programmable.
The Receive System Interface Bus Controller accepts a receive clock (RSCLK), receive address (RADR[7:0]), and
receive enable (
REN). It outputs a receive data bus consisting of receive data (RDATA[31:0]), receive parity
(RPRTY), and receive start of cell (RSOX), as well as, receive direct cell available (RDXA) and receive polled cell
available (RPXA) signals. The receive data bus is used to transfer cell data whenever one of the ports is selected
for cell data transfer. RSOX is asserted during the first transfer of a cell, cell data is transferred on RDATA, and the
data bus parity is indicated on RPRTY. All signals are sampled or updated using RSCLK. The data bus is always
driven. The RDXA and RPXA signals are used to indicate when the Receive FIFO has a programmable number of
cells available for transfer. There is an RDXA for each port in the device. RDXA goes high when the associated
port's Receive FIFO contains more than a programmable number of cells. RDXA goes low when the associated
port's Receive FIFO is empty (does not contain any cell ends). RPXA reflects the current status of a port's RDXA
signal when the port is polled. The RPXA signal is always driven.
10.6.6.3 POS-PHY Level 2, Transmit Side
In POS-PHY Level 2, the Link layer device pushes packets across the system interface. The Link layer device
polls the individual ports of the DS318x to determine which ports have space available for packet data, and selects
a port for packet data transfer. More than one PHY layer device can be present on a POS-PHY Level 2 bus.
The Transmit System Interface Bus Controller accepts a transmit clock (TSCLK), transmit address (TADR[4:0]),
transmit enable (
TEN), and a transmit data bus consisting of transmit data (TDATA[31:0]), transmit parity (TPRTY),
transmit start of packet (TSOX), transmit end of packet (TEOP), transmit error (TERR), and transmit modulus
(TMOD[1:0]). It outputs transmit direct packet available (TDXA), transmit polled packet available (TPXA), and
transmit selected packet available (TSPA) signals. The transmit data bus is used to transfer packet data whenever
one of the ports is selected for packet data transfer. TSOX is asserted during the first transfer of a packet, TEOP is
asserted during the last transfer of a packet, TERR is asserted when a packet has an error, TMOD indicates the
number of bytes transferred on TDATA during the last transfer of a packet, packet data is transferred on TDATA,
and the data bus parity is indicated on TPRTY. All signals are sampled and updated using TSCLK. The TDXA,
TPXA, and TSPA signals are used to indicate when the Transmit FIFO has space available for a programmable
number of bytes. There is a TDXA for each port in the device. TDXA goes high when the associated port's
Transmit FIFO has space available for more than a programmable number of bytes. TDXA goes low when the
associated port's Transmit FIFO is full. TPXA reflects the current status of a port's TDXA signal when the system
interface is in polled mode. TSPA reflects the current status of a port's TDXA signal when the port is selected. The
TSPA signal is tri-stated unless
TEN is asserted (low) and one of the ports is selected for packet data transfer. The
TPXA signal is tri-stated unless one of the ports is being polled for FIFO fill status.
10.6.6.4 POS-PHY Level 3 (or SPI-3), Transmit Side
In POS-PHY Level 3 (or SPI-3), the Link layer device pushes packets across the system interface. The Link layer
device polls the individual ports of the DS318x to determine which ports have space available for packet data, and
selects a port for packet data transfer. Only one PHY layer device can be present on a POS-PHY Level 3 (or SPI-
3) bus.
The Transmit System Interface Bus Controller accepts a transmit clock (TSCLK), transmit enable (
TEN), and a
transmit data bus consisting of transmit data (TDATA[31:0]), transmit parity (TPRTY), transmit start of packet
(TSOX), transmit end of packet (TEOP), transmit error (TERR), transmit start of transfer (TSX), and transmit