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Ethernet Module
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
11-19
The MII_SPEED field must be programmed with a value to provide an E_MDC frequency of less than or
equal to 2.5 MHz to be compliant with the IEEE MII specification. The MII_SPEED must be set to a
non-zero value in order to source a read or write management frame. After the management frame is
complete, the MSCR register may optionally be set to zero to turn off the E_MDC. The E_MDC generated
will have a 50% duty cycle except when MII_SPEED is changed during operation. Change will take effect
following either a rising or falling edge of E_MDC.
If the system clock is 50 MHz, programming this register to 0x0000_000A results in an E_MDC frequency
of 25 MHz * 1/10 = 2.5 MHz.
shows optimum values for MII_SPEED as a function of system
clock frequency.
11.5.9
FIFO Receive Bound Register (FRBR)
FRBR is a read-only register used to determine the upper address boundary of the FIFO RAM. Drivers can
use this value, along with the registers FRSR and TFSR, to appropriately divide the available FIFO RAM
between the transmit and receive data paths. The value in this register must be added to MBAR + 0x800
to determine the absolute address.
Table 11-15. Programming Examples for MSCR Register
System Clock Frequency
[MII_SPEED]
E_MDC frequency
25 MHz
0x3
2.08 MHz
33 MHz
0x4
2.06 MHz
50 MHz
0x5
2.5 MHz
66 MHz
0x7
2.36 MHz
31
16
Field
—
Reset
0000_0000_0000_0000
R/W
Read only
15
11
10
2
1
0
Field
—
R_BOUND
—
Reset
0000_0
110_0000_00
00
R/W
Read only
Addr
MBAR + 0x884
Figure 11-13. FIFO Receive Bound Register (FRBR)
Table 11-16. FRBR Field Descriptions
Bits
Name
Description
31–11
—
Reserved, should be cleared.
10–2
R_BOUND
End of FIFO RAM. This field contains the ending address of the FIFO RAM, exclusive.
1–0
—
Reserved, should be cleared.
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