Samsung S3C2500B User Manual page 349

S3C2500B ETHERNET CONTROLLER
7.5.1.2 Destination Address Format
Bit 0 of the destination address is an address type designation bit. It identifies the address as either an individual
or a group address. Group addresses are sometimes called 'multicast' addresses and individual addresses are
called 'unicast' addresses. The broadcast address is a special group address in the special hex format: FF-FF-
FF-FF-FF-FF.
Bit 1 of the destination address distinguishes between locally or globally administered addresses. For globally
administered or universal (U) addresses, the bit value is '0'. If an address is to be assigned locally, you must set
this bit to '1'. For the broadcast address, this bit must also be set to '1'.
7.5.1.3 Transmitting a Frame
To transmit a frame, the transmit enable bit in the transmit control register must be set and the transmit halt
request bit must be zero. In addition, the halt immediate and halt request bits in the MAC control register must be
'0'. These conditions are normally set after any BDMA controller initialization has occurred.
The transmission state machine starts transmitting the data in the FIFO, and will retain the first 64 bytes until
after this station has acquired the net. At that time, the transmitter requests more data and transmits it until the
signalling the end of data to be transmitted. The transmitter appends the calculated CRC to the end of the frame.
A frame transmit operation can be subdivided into two operations,
1) MII transmit interface operation, and 2) BDMA/ MAC transmit interface operation.
7.5.1.3.1. MII Transmit Operation
The transmitter block consists of three state machines: the gap-ok state machine, the back-off state machine,
and the main transmission state machine.
The gap-ok state machine
The gap-ok state machine tracks and counts the inter-gap timing between the frames. When not operating in full-
duplex mode, it counts 96 bit times from the de-assertion of the carrier sense (CrS) signal. If there is any traffic
within the first 64 bit times, the gap-ok state machine reset itself and starts counting from zero.
If there is any traffic in the last 1/3 of the inter-frame gap, the gap-ok state machine continues counting.
Following a successful transmission, a gap-ok is sent at the end of the next 96-bit times, regardless of the
network traffic.
In full-duplex mode, the gap-ok state machine starts counting at the end of the transmission and the gap-ok
signal is sent at the end of the 96 bit times, regardless of the network traffic.
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