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Posts: 17
Registered: ‎03-24-2017

Using internal and external oscillator c8051f320

 

I am trying to use and external oscillator (my first time to use external oscillator) (around 24 MHz) with C8051f320 which I want to use for the system clock. But I want to use the internal clock as the source for 4x multiplier for the USB clock section and the timers also. Is it possible to use both clocks in this way?

Does silabs introduce any type of external oscillator for this type of micro that matches its characteristics ?

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Hero</font></font> </a> jmg
Posts: 1,155
Registered: ‎04-27-2004

Re: Using internal and external oscillator c8051f320


...  with C8051f320

Why use the older C8051F320  ?  EFM8UB1/UB2  are lower cost.

 

The Clock fields  

 USBCLK : USB Clock Source Select Bits.

 CLKSL : System Clock Source Select Bits

show what is possible in the clock sources, and it also says this too

"When operating as a low speed function, the USB clock must be 6 MHz. When operating as a full speed function, the USB clock must be 48 MHz."

 


Does silabs introduce any type of external oscillator for this type of micro that matches its characteristics ?


Not sure what you mean ?  What oscillator specs do you require ?  MHz / ppm / Icc ?

 

Silabs have Si5351A , which is i2c programmable with external crystal for any-freq PLL.

They also have Si5121x, pre configured also with external crystal.

They did have MEMS OSC parts like Si50x, but those were EOL'd (Digikey still show stocks of some, if you do not need many...)

 

Silabs have also just released what they call Si54x Ultra Series oscillators, which are single package oscillators, but those have very low jitter, and have prices and Icc outside general USB apps.

 

 

Posts: 17
Registered: ‎03-24-2017

Re: Using internal and external oscillator c8051f320

Thank you for your reply. I already bought the evaluation board and did a lot so difficult to change.

About the oscillator, I meant specs like the drive current and load capacitance (if it is important). I need to use crystal oscillator and I meant if silabs suggests a type of crystal oscillator for this micro (For example from another vendor.) There are a lot of 24 MHz oscillators in the market with different specs. I am afraid if some of the specs make them incompatible with f320 (As I said I am new with crystal oscillator.)

 

Best 

Raja

Posts: 8,081
Registered: ‎08-13-2003

Re: Using internal and external oscillator c8051f320

[ Edited ]

About the oscillator, I meant specs like the drive current and load capacitance (if it is important). I need to use crystal oscillator and I meant if silabs suggests a type of crystal oscillator for this micro (For example from another vendor.) There are a lot of 24 MHz oscillators in the market with different specs. I am afraid if some of the specs make them incompatible with f320 (As I said I am new with crystal oscillator.)

 

you are caught in the SiLabs mumbo-jumbo regarding this.

 

When SiLabs state "external crystal oscillator" they mean "external crystal with the internal oscillator".  Any crystal except overtone crystals that I know of will work with the correct burden caps and the crystal and caps placed within 10mm of the chip

 

it is,also possible to actually use an external oscillator.

erik
Posts: 17
Registered: ‎03-24-2017

Re: Using internal and external oscillator c8051f320

So, you mean if I use the external oscillator  crystal with the chip, I should select the configurations for the internal oscillator section in the code?

 

And as my last question, how can we find out the appropriate values for caps with the crystal? Do we need the 10M resistor with the config?

 

Thanks very much 

Posts: 8,081
Registered: ‎08-13-2003

Re: Using internal and external oscillator c8051f320

[ Edited ]

So, you mean if I use the external oscillator  crystal with the chip, I should select the configurations for the internal oscillator section in the code?

no, see the datasheet

SFR Definition 13.3. OSCXCN: External Oscillator Control

and

The external oscillator circuit may drive an external crystal, ....  A CMOS clock may also provide a clock input. For a crystal or ceramic resonator configuration, the crystal/resonator must be wired across the XTAL1 and XTAL2 pins as shown in Option 1 of Figure 13.1. A 10 Mresistor also must be wired across the XTAL1 and XTAL2 pins for the crystal/resonator configuration..... The type of external oscillator must be selected in the OSCXCN

 

And as my last question, how can we find out the appropriate values for caps with the crystal? Do we need the 10M resistor with the config?

datasheet for the crystal

 

erik
Posts: 17
Registered: ‎03-24-2017

Re: Using internal and external oscillator c8051f320

Thank you very much.

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Hero</font></font> </a> jmg
Posts: 1,155
Registered: ‎04-27-2004

Re: Using internal and external oscillator c8051f320


I need to use crystal oscillator and I meant if silabs suggests a type of crystal oscillator for this micro (For example from another vendor.) There are a lot of 24 MHz oscillators in the market with different specs.

So we have a reply to MHz =  24.000 MHz, 

What ppm or precision do you need ? What is this used for ?

What package do you want ?  Small SMD, or something larger and easier to handle ?

What volumes will you make ? Does it need to pass RFI testing ?

 

For external Frequency elements, there are multiple choices :

These need Crystal Oscillator configuration :

Search Digikey for Crystals (eg 2118 hits) , or Resonators (36 hits)

 

Crystals - Need Caps and Bias R, good to some tens of ppm

Resonators - commonly have caps included, need Bias R, good to fractions of 1%

 

One caution: Going smaller usually means higher (worse) series resistance.

See the ESR (Equivalent Series Resistance) column in Digikey's lists

 

Then, getting cheaper these days are actual oscillator modules, MEMS or Crystal.

Search Digikey for Oscillators (2206 hits)

These need Vcc, need a few mA of power, and output either CMOS or Clipped Sine 

CMOS output ones can connect as per External CMOS in the data.

 

Clipped sine are more specialized, and commonly come in GPS related frequencies.

 

These have appeal if you want lowest ppm, and better RFI, as well as low Icc.

To complicate things a little, these clipped sine sources need to be AC(series cap) coupled to XTAL1, with RBias in place, and Crystal amplifier enabled.

Silabs do not currently spec/qualify the MCUs for Clipped Sine, but I've suggested they do this.

 

Posts: 17
Registered: ‎03-24-2017

Re: Using internal and external oscillator c8051f320

I need it for a simple project (Sampling voice). So i think precision  is not much important. I use a small SMD (MLP28) and it odes not need to pass RFI testing. Also if I want to use crystal oscillators in the datasheets available in digikey I cant find the volume of caps.

 

 

<a href="http://community.silabs.com/t5/Welcome-and-Announcements/Community-Ranking-System-and-Recognition-Program/m-p/140490#U140490"><font color="#000000"><font size="2">Hero</font></font> </a> jmg
Posts: 1,155
Registered: ‎04-27-2004

Re: Using internal and external oscillator c8051f320

If you do not have a Scope or easy means to measure frequency, it may be simplest and easiest to use a Oscillator module. Less total parts count.

I quite like the SiTime ones that come in SOT23-5 gull wing SMD, as being easy to develop with.

Digikey shows stock of 

SIT2001BI-S2-33E-24.000000G  3.3V ±25ppm -40°C ~ 85°C 4.5mA