MPC8308CVMADDA datasheet(19/88 Pages) FREESCALE

19 / 88 page

MPC8308 PowerQUICC II Pro Processor Hardware Specification, Rev. 1

Freescale Semiconductor

Ethernet: Three-Speed Ethernet, MII Management

Figure 11 shows the RGMII AC timing and multiplexing diagrams.

Figure 11. RGMII AC Timing and Multiplexing Diagrams

Clock cycle duration 3

tRGT

7.2

8.0

8.8

Duty cycle for 1000Base-T 4, 5

tRGTH/tRGT

Duty cycle for 10BASE-T and 100BASE-TX 3, 5

tRGTH/tRGT

Rise time (20%–80%)

tRGTR

—

0.75

Fall time (20%–80%)

tRGTF

—

0.75

GTX_CLK125 reference clock period

tG12

—8.0

—

GTX_CLK125 reference clock duty cycle

tG125H/tG125

—

Notes:

1. Note that, in general, the clock reference symbol representation for this section is based on the symbols RGT to represent

RGMII timing. For example, the subscript of tRGT represents the RGMII receive (RX) clock. Note also that the notation for rise

(R) and fall (F) times follows the clock symbol that is being represented. For symbols representing skews, the subscript is

skew (SK) followed by the clock that is being skewed (RGT).

2. This implies that PC board design requires clocks to be routed such that an additional trace delay of greater than 1.5 ns is

added to the associated clock signal.

3. For 10 and 100 Mbps, tRGT scales to 400 ns ± 40 ns and 40 ns ± 4 ns, respectively.

4. Duty cycle may be stretched/shrunk during speed changes or while transitioning to a received packet's clock domains as long

as the minimum duty cycle is not violated and stretching occurs for no more than three tRGT of the lowest speed transitioned

between.

5. Duty cycle reference is 0.5*LVDD

6. This symbol is used to represent the external GTX_CLK125 and does not follow the original symbol naming convention.

Table 25. RGMII AC Timing Specifications (continued)

At recommended operating conditions with LVDD of 2.5 V ± 5%.

GTX_CLK

tRGT

tRGTH

tSKRGT

TX_CTL

TXD[8:5]

TXD[7:4]

TXD[9]

TXERR

TXD[4]

TXEN

TXD[3:0]

(At Transmitter)

TXD[8:5][3:0]

TXD[7:4][3:0]

TX_CLK

(At PHY)

RX_CTL

RXD[8:5]

RXD[7:4]

RXD[9]

RXERR

RXD[4]

RXDV

RXD[3:0]

RXD[8:5][3:0]

RXD[7:4][3:0]

RX_CLK

(At PHY)

tSKRGT

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