Specifications

DP83848Q-Q1

SNLS341C –MARCH 2011–REVISED MARCH 2015

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5.6.2.5 RMII and Bypass Register (RBR)

This register configures the RMII Mode of operation. When RMII mode is disabled, the RMII functionality is

bypassed.

Table 5-22. RMII and Bypass Register (RBR), addresses 0x17h

BIT BIT NAME DEFAULT DESCRIPTION

15:6 RESERVED 0, RO RESERVED: Writes ignored, read as 0.

5 RMII_MODE Strap, RW Reduced MII Mode:

0 = Standard MII Mode.

1 = Reduced MII Mode.

4 RMII_REV1_0 0, RW Reduced MII Revision 1.0:

0 = (RMII revision 1.2) CRS_DV will toggle at the end of a packet to indicate

deassertion of CRS.

1 = (RMII revision 1.0) CRS_DV will remain asserted until final data is transferred.

CRS_DV will not toggle at the end of a packet.

3 RX_OVF_STS 0, RO RX FIFO Over Flow Status:

0 = Normal.

1 = Overflow detected.

2 RX_UNF_STS 0, RO RX FIFO Under Flow Status:

0 = Normal.

1 = Underflow detected.

1:0 ELAST_BUF[1:0] 01, RW Receive Elasticity Buffer:

This field controls the Receive Elasticity Buffer which allows for frequency variation

tolerance between the 50 MHz RMII clock and the recovered data. The following

values indicate the tolerance in bits for a single packet. The minimum setting

allows for standard Ethernet frame sizes at +/-50ppm accuracy for both RMII and

Receive clocks. For greater frequency tolerance the packet lengths may be scaled

(i.e. for +/-100ppm, the packet lenths need to be divided by 2).

00 = 14 bit tolerance (up to 16800 byte packets)

01 = 2bit tolerance (up to 2400 byte packets)

10 = 6bit tolerance (up to 7200 byte packets)

11 = 10 bit tolerance (up to 12000 byte packets)

5.6.2.6 LED Direct Control Register (LEDCR)

This register provides the ability to directly control the LED output. It does not provide read access to the

LED.

Table 5-23. LED Direct Control Register (LEDCR), address 0x18h

BIT BIT NAME DEFAULT DESCRIPTION

15:5 RESERVED 0, RO RESERVED: Writes ignored, read as 0.

4 DRV_LNKLED 0, RW 1 = Drive value of LNKLED bit onto LED_LINK output.

0 = Normal operation.

3:2 RESERVED 0, RO RESERVED: Writes ignored, read as 0. Value to force on LED_LINK output.

1 LNKLED 0, RW Value to force on LED_LINK output.

0 RESERVED 0, RO RESERVED: Writes ignored, read as 0.

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