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Functional Description
207
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
System Control
•
Gated system clock (SysClk): The SysClk signal acts as the clock source to the CSRs of the Ethernet
MAC. The SysClk frequency for run, sleep, and deep-sleep modes is programmed in the System
Control module.
•
MOSC: A gated version of the MOSC clock is provided as the Precision Time Protocol (PTP) reference
clock (PTPREF_CLK). The MOSC clock source can be a single-ended source on the OSC0 pin or a
crystal on the OSC0 and OSC1 pins. When advanced timestamping is used and the PTP module has
been enabled by setting the PTPCEN bit in the EMACCC register, the MOSC drives PTPREF_CLK.
PTPREF_CLK has a minimum frequency requirement of 5 MHz and a maximum frequency of 25 MHz.
See
for more information.
•
EN0RXCK: This clock signal is driven by the external PHY oscillator and is either 2.5 or 25 MHz
depending on whether the device is operating at 10 or 100 Mbps.
•
EN0TXCK: This clock signal is driven by the external PHY oscillator and is either 2.5 or 25 MHz
depending on whether the device is operating at 10 or 100 Mbps.
4.1.5.2.1.3.3 RMII Interface Clocking
Three clock sources interface to the Ethernet MAC in an RMII configuration (see
for more
information):
•
Gated system clock (SysClk): The SysClk signal acts as the clock source to the CSRs of the Ethernet
MAC. The SysClk frequency for run, sleep, and deep-sleep modes is programmed in the System
Control module.
•
MOSC: A gated version of the MOSC clock is provided as the PTP reference clock (PTPREF_CLK).
The MOSC clock source can be a single-ended source on the OSC0 pin or a crystal on the OSC0 and
OSC1 pins. When advanced timestamping is used and the PTP module has been enabled by setting
the PTPCEN bit in the EMACCC register, the MOSC drives PTPREF_CLK. PTPREF_CLK has a
minimum frequency requirement of 5 MHz and a maximum frequency of 25 MHz. See
for more information.
•
EN0REF_CLK: When using RMII, a 50-MHz external reference clock must drive the reference clock
input signal (EN0REF_CLK) and the external PHY. Depending on the configuration of the FES bit in
the Ethernet MAC Configuration (EMACCFG) register, the EN0REF_CLK is divided by 20 for 10-Mbps
operation or by 2 for 100-Mbps operation and is used as the clock for receive and transmit data.
4.1.5.2.1.4 PWM Clock Control
The PWMCC register can be used to select the system clock as the PWM clock source or a divided
system clock. For more information, see
.
4.1.5.2.1.5 Other Peripheral Clock Control
In the UART and QSSI Clock Control registers, users can choose between the system clock (SysClk),
which is the default source for the baud clock, and an alternate clock. There may be special
considerations when configuring the baud clock.
4.1.5.2.2 Optional Clock Output Signal (DIVSCLK)
An optional clock output, DIVSCLK, can be used as a clock source to an external device but bears no
timing relationship to other signals. DIVSCLK is not synchronized to the system clock. By programming
the SRC field in the Divisor and Source Clock Configuration (DIVSCLK) register, the following clock
outputs can be selected for DIVSCLK:
•
System clock
•
PIOSC
•
MOSC
The DIV field in the DIVSCLK register controls the divided output clock frequency. The DIVSCLK signal is
selected as an alternate function of a GPIO signal and has the electrical characteristics of a GPIO (see
the device-specific data sheet).