SYSCLK4
SYSCLK7
PLL Controller 0
LPSC
EMAC
1000 0000
PINMUX15[3:0]
RMII_MHZ_50_CLK
Signal
50 MHz Reference Clock
On Chip
0000 1000
3-State
Peripheral Clocking
125
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Device Clocking
6.3.4 EMAC Clocking
The EMAC module sources its peripheral bus interface reference clock from PLL0_SYSCLK4 that is at a
fixed ratio of the CPU clock. The external clock requirement for EMAC varies with the interface used.
When the MII interface is active, the MII_TXCLK and MII_RXCLK signals must be provided from an
external source. When the RMII interface is active, the RMII 50 MHz reference clock is sourced either
from an external clock on the RMII_MHZ_50_CLK pin or from PLL0_SYSCLK7 (as shown in
).
The PINMUX15_3_0 bits in the pin multiplexing control 15 register (PINMUX15) of the System
Configuration Module control this clock selection:
•
PINMUX15_3_0 = 0: enables sourcing of the 50 MHz reference clock from an external source on the
RMII_MHZ_50_CLK pin.
•
PINMUX15_3_0 = 8h: enables sourcing of the 50 MHz reference clock from PLL0_SYSCLK7. Also,
PLL0_SYSCLK7 is driven out on the RMII_MHZ_50_CLK pin.
shows example PLL register settings and the resulting PLL0_SYSCLK7 frequencies based on
the OSCIN reference clock frequency of 25 MHz.
Figure 6-5. EMAC Clocking Diagram
NOTE:
The SYSCLK7 output clock does not meet the RMII reference clock specification of
50 MHz +/-50 ppm.