Uno R4 schematic

[davehart292]

1. Schematic shows 16mhz main oscillator crystal. This appears not fitted. Should that be indicared on schematic?
2. 16mhz is too fast for PLL input, would 12mhz be better?
3. Schematic shows USB_VBUS detecting +5v. Should this be connected to VUSB?

[awneil]

@davehart292

16mhz

* 16MHz

@davehart292

• This appears not fitted. Should that be indicared on schematic?

It appears that they don't bother to identify "Do Not Fit" / "Do Not Populate" parts:

USB connector switch

Thanks, I agree with you. As a last test now also having done a cold ohm/resistance measurement, there is only a 5 Mega-ohm (thus NO) connection to either ESP or RA4 between USB pins. That leaves 3 issues: The schematics need to be updated to reflect "do not populate" The documentation needs to be updated to reflect that 21 instead of 40 should be used for SW USB switch. The documentation needs to include a warning NOT to apply the USB HW and SW switch at the same time, as pulling P408 LOW wi…

[jojo]

Hello, can you share the screenshot of the part from the schematic where it is mentioned?

[tonynyny]

I think is this part because I have the same question ^^

[awneil]

@tonynyny

I have the same question

here:

Uno R4 minima quartz or not

Hello all. When I look at the r4 minimim schematics, I see a 16Mhz quartz on it, but this board presentation says it works at 48 Mhz. So what's true ? Is it really a 16 Mhz quartz on the board ? If yes, does the board really running at 48 Mhz ? Thanks [image]

[jojo]

Thank you for reporting this, we noticed that this is an error with the interactive viewer. Please refer to the schematics under the download section.

[awneil]

@jojo

this is an error with the interactive viewer

So does that also apply to the issue with the USB switch in the linked thread?

[tonynyny]

@jojo
can you please post the link for downloading it ?
I only found the v1.0 version of the schematic

[ptillisch]

@tonynyny the schematics for each board are available for download from the "Resources" section of its documentation page.

Open this page and then click the "Schematics" download link you find there:

https://docs.arduino.cc/hardware/uno-r4-minima#resources

[ptillisch]

Ah, from your edit it seems that maybe you already found it.

[tonynyny]

yes, but it is the same schematics than the post 4 picture I send....

[davehart292]

Thankyou everyone for your comments.
I think the Arduino concept is brilliant for learning microcontrollers, and part of that should be wading throught the datasheets an schematics for deeper understanding. Maybe Arduino are a little lax with the Uno R4 documentation?
The 16mhz crystal exceeds maximum PLL input frequency (12.5mhz) and with that crystal could only run at max 16mhz.
My understanding of the CAN bus is that it needs stable accurate oscillator, therefore the R4 might not be a good platform for CAN bus?
![Screenshot_20230825-232444_Drive|550x500]

[alranel]

@davehart292 The downloadable schematics should be complete and accurate. The issue you're seeing is not with our documentation but with the interactive viewer widget which has a limitation and does not allow us to select which variant of the Altium project shall be displayed so it shows the full one including components that aren't being mounted. We reported this to Altium and we hope they will take an action. Meanwhile, we're considering adding a note close to the viewer. Please refer to the downloadable schematics and let us know if you spot any error - we'll fix it promptly. Thank you

[awneil]

@alranel

The issue you're seeing is not with our documentation

I think it is!

@alranel

it shows the full one including components that aren't being mounted

Your schematics should have a note on components that may not be fitted - this is standard practice.

[gpb01]

@alranel:

Hi Alessandro,

sorry, but, on the product page if i click on the box "SCHEMATICS IN PDF" I end up on THIS pdf.

Now, in the pdf, I see:

I bought three "Arduino UNO R4 Minima" and all three look like this:

... I see neither a crystal nor a ceramic resonator nor the necessary capacitors but only tinned pads

Also the picture form the product reference page shows the same situation:

... so it seems that the boards do not use an external crystal, but the internal oscillator ... can you confirm this or indicate where such a crystal is?

Thnaks in advance,

Guglielmo

[susan-parker]

@gpb01

... so it seems that the boards do not use an external crystal, but the internal oscillator ...

Hum, it appears that the Minima is using the internal "High-speed on-chip oscillator (HOCO)", with the speed selected in the Option Function Select Register 1 (OFS1) :
HOCO Frequency Setting 1: HOCOFRQ1[2:0] = 100b: i.e. 48 MHz
See datasheet section 6.2.2 page 106

These are the Minima system clock settings at the beginning of start(), after the serial is initialized.

OPTION_OFS1      - FFFFCEDF // HOCO Frequency Setting xxxxCExx = 48 MHz, HOCO Oscillation Enabled
SYSTEM_SCKDIVCR  - 10010100 // System Clock Division Control Register; PCKB = 1/2
SYSTEM_SCKSCR    - 0  // Clock Source Select = HOCO
SYSTEM_PLLCR     - 1  // PLL Stop Control; 1 = PLL is stopped
SYSTEM_PLLCCR2   - 7  // PLL Freq Multp; 7 = ×8, PLL Out Freq Div Ratio Sel = 00: Reserved !!!
SYSTEM_MEMWAIT   - 1  // Memory Wait Cycle Select; 1 = Wait
SYSTEM_MOSCCR    - 1  // Main Clock Oscillator Stop; 1 = Main clock oscillator is stopped
SYSTEM_HOCOCR    - 0  // HOCO Stop; 0 = Operate the HOCO clock i.e. HOCO clock is running
SYSTEM_MOCOCR    - 0  // MOCO Stop; 0 = Operate the MOCO clock i.e. MOCO clock is running
SYSTEM_OSCSF     - 1  // HOCO Clock Oscillation Stabilization Flag; 1 = The HOCO clock is stable
SYSTEM_CKOCR     - 84 // Clock Out Source Select = SOSC at x1 (no-division), Enabled 
SYSTEM_TRCKCR    - 1  // Trace Clock Operation Frequency Select; 1 = value after reset
SYSTEM_OSTDCR    - 0  // Oscillation Stop Detection Interrupt = Disabled
SYSTEM_OSTDSR    - 0  // Oscillation Stop Detection Flag; 0 = Main clock oscillation stop not detected
SYSTEM_SLCDSCKCR - 0  // LCD Source Clock; 0 = LOCO but LCD source clock out disabled
SYSTEM_MOCOUTCR  - 0  // MOCO User Trimming, 0 = Center Code i.e. none
SYSTEM_HOCOUTCR  - 0  // HOCO User Trimming, 0 = Center Code i.e. none
SYSTEM_MOSCWTCR  - 9  // Main Clock Oscillator Wait Control Register; 9 = Wait time of 262144 cycles (32768 μs).
SYSTEM_HOCOWTCR  - 5  // HOCO Wait Time Setting; 5 = Wait time is 287 cycles (35.875 μs) ???
SYSTEM_USBCKCR   - 1  // USB Clock Source Select; 1 = HOCO
SYSTEM_MOMCR     - 8  // Main Clock Oscillator Drive Capability; 1 = 1 MHz to 10 MHz
SYSTEM_SOSCCR    - 0  // Sub-Clock Oscillator Stop; 0 = Operate the sub-clock oscillator
SYSTEM_SOMCR     - 0  // Sub-Clock Oscillator Drive; 0 = Normal mode 
SYSTEM_LOCOCR    - 0  // LOCO Stop; 0 = Operate the LOCO clock
SYSTEM_LOCOUTCR  - 0  // LOCO User Trimming, 0 = Center Code i.e. none

Note registers are in ascending address order, not as listed in datasheet.

[gpb01]

@susan-parker

Hum, it appears that the Minima is using the internal "High-speed on-chip oscillator (HOCO)

Thanks Susan,
yes, since there is no crystal on the board, I assumed so , but my question to @alranel was intended to raise the issue of a probable error in the schematic ...

Guglielmo

[susan-parker]

@gpb01

but my question to @alranel was intended to raise the issue of a probable error in the schematic ...

Indeed, and I understood it as such.

Just decided to work out the clock settings to confirm what was being done, as there was also a question about CAN bus and if the internal clock would be good enough.

As an aside this also confirms that the schematic is inaccurate in that although the PCB is laid out for these components they are not fitted and so as per previous posts should ideally be shown as not-fitted (as is done with the I2C pullups R1 & R2).

5.6 HOCO Accuracy
The internal high-speed on-chip oscillator (HOCO) runs at ... 24 MHz, 32 MHz, 48 MHz, or 64 MHz for Arm Cortex-M4 devices, with a typical accuracy of +/-2% or better. HOCO accuracy specifications are characterized for various ambient operating temperature (Ta) ranges.

https://www.renesas.com/us/en/document/apn/ra4-quick-design-guide

I haven't had much to do with the CAN bus, so don't know how picky it is with clock stability.

[awneil]

@susan-parker

they are not fitted and so as per previous posts should ideally be shown as not-fitted

Exactly!

[tonynyny]

Thank you for taking the time for this analysis.
I'll soon buy a minima, so I hope there is no big error on it so I can use all function promised by arduino ^^

About schematics, if someone knows something about question here
https://forum.arduino.cc/t/minima-schematics-understanding/1161523?u=tonynyny
I'll be very happy to know