NXP Semiconductors MPC574 P Series User manual

MPC574xP Clock Calculator Guide
How to use MPC5744P tool to easily calculate device frequency domains
by: NXP Semiconductors
1 Introduction
NXP’s MPC574xP is a lockstep, dual-core 32-bit microcontroller intended for
safety and chassis applications. This application note will refer to any device
in the MPC574xP family, MPC5741P, MPC5742P, MPC5743P, and MPC5744P,
as simply “MPC5744P.”
The MPC5744P supports an 8-44 MHz external oscillator (XOSC), a 16 MHz
internal RC oscillator (IRCOSC), and two phase locked loops (PLL) for a
maximum operating frequency of 200 MHz. The IRCOSC is selected out of
reset so increasing the operating frequency from 16 MHz requires additional
configuration. The MPC574xP clock calculator is meant to complement the
reference manual. It seeks to simplify the clock configuration process by
providing a graphical, interactive tool to help the user find the correct register
settings in order to achieve the desired clock frequencies.
Accompanying this application note is the clock calculator. You can download
it from MPC574xP_Clock_Calculator.
The clock calculator makes use of macros to perform functions like resetting
the spreadsheet to initial values, configuring all clock frequencies to the
maximum allowable settings, and copying generated code. Macros must be
enabled in the user's MS Excel to access these features. If macros are turned
off however, the tool will still be able to calculate clock frequencies, but the
aforementioned features will be disabled. To turn on macros in MS Excel 2016,
go to the Developer tab on the top toolbar and click on Macro Security. A popup
window will appear. In it, select Enable all macros.
Figure 1. Enabling macros
Contents
1 Introduction..........................................1
2 Clock calculator design...................... 2
2.1 Tree......................................... 3
2.2 Oscillator control..................... 6
2.3 Peripheral domains................. 6
2.4 LFAST clocking....................... 7
2.5 PLLx........................................9
2.6 Reference Tables
(pll0_phi, pll0_phi1, and
pll1_phi)...................................9
2.7 Summary...............................10
2.8 Limits.....................................13
3 Clock tool example use case:
configure ADC to PLL0 at 80 MHz. 14
3.1 Configure ADC_CLK............. 15
3.1.1 Configure the
oscillator.................... 16
3.1.2 Configure PLL0.......18
3.1.3 Finish setting
ADC_CLK..................23
3.2 Configure ADC bus clock
to 40 MHz PLL.......................24
3.3 Observe the registers............25
3.4 Copy the code.......................26
4 Conclusion......................................... 27
5 Revision history.................................27
NXP Semiconductors Document Number: AN5393
Application Note Rev. 9, April 2018

2 Clock calculator design
The MPC574xP clock calculator takes the form of an interactive Microsoft Excel spreadsheet organized into multiple tabs as shown
in the following figure.
Figure 2. MPC574xP clock calculator setup
Clock sources (e.g. oscillators and PLLs) propagate to the various clock domains from which the MCU modules take their clocks.
Most cells representing clock domain frequencies are not to be modified manually. The user is meant to enter frequencies to the
few select clock sources and all clock domain frequencies derive from these sources. Several clock domain inputs are meant to
be modified manually as they represent external clocks that are driven into a pin. There are also input cells that set muxes and
clock dividers. All cells that take entries have blue borders instead of black, shown below.
Figure 3. Input cells vs. output cells
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There are limits to what frequencies can be entered to the input frequency cells. Values that are out of range will be rejected and
the user will receive an error message. Invalid clock domain frequencies that arise from valid input values and legal, but improper,
dividers will be shaded in red, as will be explained in greater depth later in this application note.
Frequency values are linked across tabs, so FRAY_CLK in the Tree tab will always be the same as FRAY_CLK in the Peripheral
Domains tab. Hyperlinks are provided to duplicate domain names to link back to their points of origin. For example, FRAY_CLK
originates in Tree. Therefore, clicking the FRAY_CLK textbox in Peripheral Domains will take the user to FRAY_CLK in Tree.
Textboxes that are links, when hovered over, will cause the mouse cursor to turn into a hand icon and a pop-up to appear showing
the address of the destination, as shown in the following figure.
Figure 4. Clicking on a link
The following subsections will explain in depth the purpose of each tab.
2.1 Tree
Tree is the centerpiece of the tool. This tab is the starting point for all clock frequency calculations. It is organized to resemble the
MPC5744P clock tree as presented in the following figure.
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Figure 5. MPC5744P Reference Manual clock tree
The following figure shows, in part, the diagram’s clock tool counterpart. The difference between the two is that the latter is
interactive.
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Figure 6. Clock calculator tree
The flow of the diagram generally goes from left to right. On the left are the MPC5744P clock sources and on the right are the
clock domains. MCU modules run on one or more of these clock domains.
Clock domain frequency values are displayed in the outlined cells next to their labels. Most cells are not meant to be written to;
their values are dependent on the frequencies generated by preceding steps in the clock tree. Take MOTC_CLK, for example: its
value is sourced from either the IRCOSC, XOSC, or PLL0_PHI. Now, look at the IRCOSC block. IRCOSC is at 16 MHz, but the
frequency that propagates depends on the next block, IRCOSC Source Controller. Therefore, the actual input frequency received
by blocks that take IRCOSC as a source is the IRCOSC frequency of 16 MHz, filtered by the IRCOSC Source Controller block.
The same goes for XOSC. PLL0_PHI is configured in the PLL0 tab. MOTC_CLK selects from these three clock sources by selecting
the value of the AUX Clock Selector 0 block. Then finally, the selected signal is divided by the MOTC_CLK prescaler value.
Each auxiliary clock and the system clock can feed into multiple domains that each have their own dividers. The number to the
left of the prescaler shows the number of the divider that is associated with that clock. In the case of MOTC_CLK, the number “0”
is shown next to the MOTC_CLK divider. This means that MOTC_CLK is configured by Divider 0 of Auxiliary Clock 0.
This tab also features two buttons, Reset and Max. They only have function when macros are enabled. Clicking on these buttons
with macros disabled will return an error. If macros are enabled, the Reset button will set all blocks to their reset value, as described
in the reference manual. The Max button sets all blocks in this tool to values that configure the system and auxiliary clock domains
to their respective maximum allowable frequencies. Below is a screenshot of the buttons.
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Figure 7. Buttons
2.2 Oscillator control
Oscillator Control controls the generation of the external oscillator (XOSC) frequency. MPC5744P supports two ways of XOSC
generation. The chip has two external oscillator pins, XTAL and EXTAL. An 8-44 MHz external oscillator can be connected to both
pins. This external oscillator is also referred to simply as the XTAL. If the XOSC Select block selects XTAL, XOSC will derive its
frequency from the 8-44 MHz external oscillator (XTAL) block. Alternatively, a waveform can be driven directly to the EXTAL pin.
This signal is also referred to simply as EXTAL. When the XOSC Select block selects EXTAL, XOSC will derive its frequency from
the EXTAL pin. Shown below is a screenshot.
Figure 8. Oscillator control
2.3 Peripheral domains
Peripheral Domains is an in-depth diagram of MPC5744P modules. Where Tree leaves off at the clock domain level, Peripheral
Domains picks up and progresses to the module level, shown below.
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Figure 9. Peripheral domains
The clock domains are color-coded. Black lines are reserved for clock domains that only a few modules use. For example, the
SAR ADC module takes both PBRIDGEx_CLK and ADC_CLK. ADC_CLK is black because only the ADC uses that clock. As a
rule of thumb, clock domains are represented with black lines if all modules using it can fit within a single window without having
to scroll. The frequencies on this tab are not meant to be modified and are dependent on frequency values in the Tree tab.
2.4 LFAST clocking
The LFAST is a versatile, but intricate module. It supports its own PLL which generates multiple phases and generates a signal
within specification only if its inputs are certain frequencies. These intricacies make it necessary to give LFAST is own dedicated
tab. Peripheral Domains still hosts an LFAST block that shows its input clocks and is hyper-linked to LFAST Clocking, as shown
in the following figure.
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Figure 10. LFAST in peripheral domains
LFAST Clocking presents a block diagram of the module with various clocks going into it. It also supports LFAST_PLL
configuration to increase the LFAST frequency up to 320 MHz. The LFAST also supports a low-speed mode as well as a high-
speed mode. This tool allows the user to select between the two modes. Below is a screenshot of the sheet.
Figure 11. LFAST block diagram
Since the LFAST signal must be generated from an input clock of 10, 13, 20, or 26 MHz, this tool blocks any input from the signal
RF_REF other than these four values. RF_REF can technically be set to any value, but any frequency that is not 10, 13, 20, or 26
MHz generates an invalid signal. Therefore, in this tool, RF_REF goes through the LFAST Input Filter block before becoming
lfast_sys_clk, which in turn is the signal that gets fed into the LFAST_PLL and phase generators, as shown in the following figure.
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Figure 12. LFAST clocking input filter
If RF_REF is 10, 13, 20, or 26 MHz, lfast_sys_clk is also 10/13/20/26 MHz; otherwise, lfast_sys_clk is 0. MPC5744P does not
actually filter RF_REF the way this tool does. The purpose of the LFAST Input Filter block is to simulate how the user can technically
set RF_REF to any value, but the resulting LFAST output would be unusable. Therefore, if a user were to enter an invalid input
frequency (i.e. not 10, 13, 20, or 26 MHz), all subsequent frequencies would be 0, and the user would know to change the input.
2.5 PLLx
PLL0 and PLL1 are visual abstractions of the PLL digital interface, as shown in the following figure.
Figure 13. PLL0 control
The input source of PLL0 and PLL1 is selected by the auxiliary clock selectors, AUX Clock Selector 3 and AUX Clock Selector
4in the Tree tab. Then, from the source, the dividers and multipliers located in the PLL0 and PLL1 tabs are set in order to achieve
the PLL output frequencies. The PLL output frequencies are in turn propagated to the PLLx_PHIn clock domains in the Tree tab.
2.6 Reference Tables (pll0_phi, pll0_phi1, and pll1_phi)
The three tabs pll0_phi, pll0_phi1, and pll1_phi are reference tables for the user to find the appropriate PLL dividers and multipliers
to achieve the desired PLL frequency. There is a tab for each PLL output because input frequencies and the range of acceptable
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divider/multiplier values differ between each other. However, they all follow the same setup. Note that Columns A, B, and C of
these tabs are frozen so if the table looks cut off, just scroll left or right.
PLL frequencies are calculated from a reference frequency, a reference divider (RFD), a multiplier (MFD), and in PLL0, a prescaler
(PREDIV). The PLL reference is not manually configurable because there are a finite number of input values the PLL can take.
For example, PLL0 can only reference either the 16 MHz IRCOSC or the 8-44 MHz XOSC. PLL reference therefore comes from
the Tree tab. Configure AUX Clock Selector 3 and AUX Clock Selector 4 in Tree for PLL0 and PLL1, respectively. Once the PLL
reference frequency is configured, enter the desired PLL output frequency. Also, enter the PREDIV value when using PLL0_PHI
or PLL0_PHI1. The reference table then calculates the output frequency for each MFD and RFD setting. Like in the other sections,
frequencies are color-coded to define which values are valid and which are not. Shading will change automatically once the output
PLL frequencies are calculated. MFD and RFD settings that achieve the exact desired frequency is marked in green; values that
exceed the desired frequency, but are within MPC5744P hardware specifications are marked in yellow; and frequencies that
exceed the MPC5744P hardware specification are colored red. Below is a screenshot of the reference table for PLL0_PHI.
Figure 14. PLL0_PHI reference table 2.6
2.7 Summary
Almost all blocks populating this clock calculator represent real register fields in silicon. The Summary tab collates all the
information from the rest of the clock calculator into a list of register values, a screenshot of which is shown in the following figure.
The values in the register summary are interactive, updating automatically when the associated block is changed. Registers listed
within Summary are only the ones whose values are affected by clock configuration, not every single register available in the SoC.
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