Motorola MCF5281, MCF5282 user manual MII Speed Control Register Mscr, Dispreamble Miispeed

Models: MCF5282 MCF5281

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Programming Model

If the MMFR register is written while frame generation is in progress, the frame contents will be altered. Software should use the MII_STATUS register and/or the MII interrupt to avoid writing to the MMFR register while frame generation is in progress.

17.5.4.7 MII Speed Control Register (MSCR)

The MSCR provides control of the MII clock (EMDC pin) frequency, allows a preamble drop on the MII management frame, and provides observability (intended for manufacturing test) of an internal counter used in generating the EMDC clock signal.

 

31

 

 

 

 

 

16

Field

 

 

 

 

 

 

 

 

 

 

 

Reset

 

0000_0000_0000_0000

 

 

 

 

 

 

 

 

 

 

R/W

 

R/W

 

 

 

 

 

 

 

 

 

 

 

 

 

15

8

 

7

6

1

0

 

 

 

 

 

 

 

Field

 

DIS_PREAMBLE

 

MII_SPEED

 

 

 

 

 

 

 

Reset

 

0000_0000_0000_0000

 

 

 

 

 

 

 

 

 

 

R/W

 

R/W

 

 

 

 

 

 

 

 

 

 

Address

 

IPSBAR + 0x1044

 

 

 

 

 

 

 

 

 

 

 

Figure 17-10. MII Speed Control Register (MSCR)

Table 17-18. MSCR Field Descriptions

Bits

Name

Description

 

 

 

31–8

Reserved, should be cleared.

 

 

 

7

DIS_PREAMBLE

Asserting this bit will cause preamble (32 1’s) not to be prepended

 

 

to the MII management frame. The MII standard allows the preamble

 

 

to be dropped if the attached PHY device(s) does not require it.

 

 

 

6–1

MII_SPEED

MII_SPEED controls the frequency of the MII management interface

 

 

clock (EMDC) relative to the system clock. A value of 0 in this field

 

 

will “turn off” the EMDC and leave it in low voltage state. Any

 

 

non-zero value will result in the EMDC frequency of

 

 

1/(MII_SPEED*2) of the system clock frequency.

 

 

 

0

Reserved, should be cleared.

 

 

 

The MII_SPEED field must be programmed with a value to provide an EMDC frequency of less than or equal to 2.5 MHz to be compliant with the IEEE 802.3 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 EMDC. The EMDC 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 EMDC).

MOTOROLA

Chapter 17. Fast Ethernet Controller (FEC)

17-31

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Motorola MCF5281, MCF5282 user manual MII Speed Control Register Mscr, Dispreamble Miispeed