Chapter 12: 10/100 IEEE802.3 Media Access Controller
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
12-49
12.5.3 MII
Interface
The MII interface is described in this section.
12.5.3.1 macxTxClk
TXCLK is the transmit clock used to provide the timing reference for the transfer of the
macxTxEn, macxTxD[3:0] and macTxEr to the PHY. The MAC handles internal
synchronization between gbsBusClk and these transmit signals.
12.5.3.2 macxRxClk
macxRxClk is the receive clock used to provide the timing reference for the transfer of the
macxRxDv, macxRxD[3:0] and macxRxEr from the PHY. The MAC handles the synchro-
nization between gbsBusClk and these receive signals.
12.5.3.3 MII Management Interface
The MAC has two 16-bit registers that are used to read and write the physical layer device.
To initiate a read of one of the MII registers, the user must write to the MII control register.
The MII control register requires a valid PHY address, a valid opcode and a valid register
address. When this register is written, MAC will initiate the read by diving MDC with a valid
clock and MDIO with the proper preamble, start code, and data from the MII control register.
The Busy bit in the MII control register is set for the duration of the operation. Data read from
the PHY are stored in the MII data register and are available for the host to read when the
Busy bit is zero. Writing to an MII register is similar. The host must never write to the MII
data register or to the MII control register while the Busy bit is set.
12.5.4 Interrupt
The MAC supports two kinds of interrupt event. One is the frame interrupt FRMINT, and the
other is the counter interrupt CNTINT. FRMINT is used mainly for notifying the CPU that a
transmission or reception error has occurred which may cause the port to stop operating
correctly. CNTINT is active when a counter overflows. CNTINT and FRMINT both share one
interrupt signal macgIntB.
12.5.5 Reset
There are two kinds of reset: Hardware Reset and Software Reset.
12.5.5.1 Hardware
Reset
When SysResetB is driven Low:
•
Registers return to their default values.
•
State machines return to their idle state.
•
Counters are reset to zero.
Содержание TMPR7901
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