W89C840F
The MAC will, finally, do the framing function to strip the preamble and the SFD before sending
the receive data to the receive DMA machine. The data sent to the receive DMA state machine includes
the LLC data and the 4 bytes CRC.
Loopback diagnostics function
The loopback mode defined for W89C840F is used for diagnostic. The transmit out data will
appear on the MII interface and will then be fed back into the internal receive channel of the MAC
block and then be moved back into the host memory by the receive DMA state machine. In loopback
mode, the transmission function will work normally as it is in normal mode, but, only the data is
processed by the MAC. The COL, CRS will be ignored in loopback mode.
To program the W89C840F into loopback mode, the Loopback Mode of C18/CNCR should be
set to 01H.
Full duplex and half duplex function
The transmit DMA and the receive DMA are independently operating no matter what the
W89C840F is set in full duplex mode or in half duplex mode. However, in MAC side, the operations
are different and depend on the full duplex or half duplex mode is selected.
In the half duplex mode, the MAC should perform the transmission or reception operation at
the different time frame. Simultaneous transmission and reception operation are not allowed. Once the
half duplex mode is selected, the MII input signals, COL and CRS , will be valid inputs for the
W89C840F. During the time the MAC is transmitting a packet, an active signal COL on MII bus will
be judged to be a transmit collision event, occurred on the media. However, in the time duration from
10 bits time to 16 bits time after the packet is transmitted, the active COL signal is recognized as a
SQE test signal but not a collision event. The active signal CRS will be recognized as a loopback
carrier sense signal when the MAC is transmitting a packet. The carrier sense lost status is relied on
the CRS. Normally, there should not be any carrier sense lost during transmitting if the media and
devices are functional.
In the full duplex mode, the MAC can perform the transmission and receive operation at the
same time. In this case, the COL and CRS signal on MII will be ignored. There are no collision event,
SQE lost and carrier sense lost defined in the full duplex mode. Any activity on COL and CRS will not
affect the operation inside the MAC.
To select the full duplex mode or the half duplex mode, you have to set the full duplex control
bit of C18/CNCR.
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ETC [ ETC ]
