8101 Datasheet, PDF (30/172 Pages) LSI Computer Systems – Gigabit Ethernet Controller

The SCLK input must continuously operate at 33–66 MHz. When RXENn
is deasserted, the receive interface is not selected and, subsequently, no
data from the receive FIFO can be output over the system interface. If
the receive watermarks RXWM1 and RXWM2 are asserted while RXENn
is deasserted, the next data word from the receive FIFO appears on the
RXD[31:0] outputs until RXENn is asserted. When RXENn is asserted,
a data word from the receive FIFO is clocked out onto the RXD[31:0]
outputs after each rising edge of the SCLK input. After the entire packet
has been clocked out, no more data is clocked out on RXD[31:0] until
RXENn is deasserted and reasserted, which allows extra dribble SCLK
clock cycles to occur after the end of the packet. RXD[31:0] output data
is a 32-bit wide packet data whose format and relationship to the MAC
packet and 10-bit PHY data is described in Figure 2.3.
The RXBE[3:0] signals determine which bytes of the 32-bit RXD[31:0]
data word contain valid data. RXBE[3:0] are clocked out on the rising
edge of SCLK along with each RXD[31:0] data word. Note that
RXBE[3:0] = 0b1111 for all words of the packet except the last word,
which may end on any one of the 4-byte boundaries of the 32-bit data
word. The correspondence between the byte enable inputs and the valid
data bytes of each data word on RXD[31:0] is defined in Table 2.2.
The RXSOF and RXEOF signals indicate which words start and end the
Ethernet data packet, respectively. These signals are generally clocked
out on the same SCLK rising edge as the first and last word of the data
packet, respectively. However, their exact position relative to the data
packet is dependent on the programming of the PEOF bit and
STSWRD[1:0] bits in Register 7, “Configuration 1”. The exact RXSOF
and RXEOF position for combinations of these two bits is shown in
Figure 2.5. More details about the definition of these bits can be found
in “Register 7–Configuration 1‚" Section 4.3.8, and more details about the
status word can be found in Section 2.14, “Receive Status Word,”.
2-12
Functional Description
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