Generating a clock input for PCM1725U

[The Master]

Hi, Im trying to test some PCM1725U chips but im not quite sure how the SCKI (system clock input) pin is supposed to work. Normally with PICs i would use a ceramic resonator or crystal and 2 capacitors. This chip only seems to have 1 pin for the clock input so im not sure how i would generate the pulse. Should i use a 555 timer or something similar?

[rsocor01]

Hi, Im trying to test some PCM1725U chips but im not quite sure how the SCKI (system clock input) pin is supposed to work. Normally with PICs i would use a ceramic resonator or crystal and 2 capacitors. This chip only seems to have 1 pin for the clock input so im not sure how i would generate the pulse. Should i use a 555 timer or something similar?

Hi,

Since you need at least 8 MHz clocking signal, then HPWM is out of the picture. Another option would be to use the CLKO feature that some PICs have like the 18F4550 on RA6. I have never used it, but according to the datasheet it can output a system cycle clock output of Fosc/4.

Well, maybe somebody else can provide a better answer.

Robert

[The Master]

Can i still use the CLKO pin while using a crystal or can i only output from the internal osc? Im not sure the internal osc can go fast enough for that and would i be able to make it prescise enough? I need 8.192MHz and not just 8MHz (or would 8MHz be suitable for this chip?)

[rsocor01]

I need 8.192MHz and not just 8MHz (or would 8MHz be suitable for this chip?)

Looking at the specs, you have a minimum of 16 KHz and a maximum of 96 KHz for the sampling frequency (see the attached picture). The corresponding minimum clocking signal for Fs=16 KHz is 4.096 MHz (256*Fs). The table that gives you the 8.192 MHz is just a list of the typical values.

Can i still use the CLKO pin while using a crystal or can i only output from the internal osc? Im not sure the internal osc can go fast enough for that and would i be able to make it prescise enough?

I am not sure either that the internal osc can go fast enough for this PCM chip. Now, if you use an external 20 MHz crystal, which is typical for this 18F4550 PIC, I don't see why it wouldn't work unless I'm missing something here. In this case, I would say that Fosc=20 MHz and the output at RA6 would be Fosc/4 = 5 MHz, which is within the allowed boundaries.

Let us know if you made it work or not.

Robert