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CHAPTER 3 FUNCTIONAL DESCRIPTION
User’s Manual S14054EJ4V0UM
56
3.8.3 Connecting
µµµµ
PD98431 MII output signal pins
To connect the MII output signals (TXD, TXEN, TXER, MDC, MDIO) to a PHY device, connect a series resistor of
18
Ω
to 27
Ω
to each MII output signal as shown in Figure 3-14, to make the driving capability of the MII output buffer
conform to the IEEE802.3u standard.
Figure 3-14. Connecting MII Output Signal Pins
µ
PD98431
18
Ω
to 27
Ω
TXD/TXEN/TXER/MDC/MDIO
External PHY device
TXD/TXEN/TXER/MDC/MDIO
3.8.4 10 Mbps serial interface
The
µ
PD98431 has a serial interface that connects a 10 Mbps transceiver. This interface consists of 1-bit serial
data, clock, and control signals for both transmission and reception.
For the transmit interface of port n, TXCLKn, TXDn[0], and TXENn are used. To detect collision, the COLn signal
is used. Transmit serial data is output from TXDn[0] at the rising edge of TXCLKn.
TXENn goes high when the data in TXDn[0] is valid.
For the receive interface of port n, RXCLKn, RXDn[0], and CRSn are used. The
µ
PD98431 samples the receive
serial data input from RXDn[0] at the rising edge of RXCLKn. If CRSn is high at this time, the
µ
PD98431 assumes
that the sampled data is valid receive data.
3.9 Flow Control
The
µ
PD98431 implements flow control by processing the pause control frame defined by IEEE802.3x Annex31B.
The purpose of flow control is to lower the frequency at which packets are transmitted from the other terminals
connected to the
µ
PD98431 on a point-to-point basis for full-duplex operation.
When a pause control frame is received, the value of the pause timer field in the control frame is loaded to the
pause timer in the MAC. If the pause timer is not 0, the next transmission is started after the time set by the pause
timer has expired.
To suppress data transmission from other terminals on the network, a reserved multicast address (01-80-C2-00-
00-01), pause op code, and a 16-bit pause timer value are generated and transmitted as a pause control frame.
3.9.1 Receiving control frame
The
µ
PD98431 validates reception and detection of a control frame when the RXFC bit of the MACC1 register is
1. The pause control frame is detected by checking the destination address and op code of the type field. In order
that the receive data stream is detected as a pause control frame, either the multicast address (01-80-C2-00-00-01)
reserved as a destination address or the unicast address given to the MAC is necessary. In addition, 8808H is
necessary for the length/type field, and the correct pause op code 0001H is necessary for the control op code field.
When the
µ
PD98431 receives a valid pause control frame, it suppresses transmission for the duration specified by
the pause timer value included in the received pause control packet.
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