I’m trying to design a peripheral cape that requires a max 16 MHz clock input. What are my options for a clock source on the P8-P9 headers? I looked at the TI datasheet for the mysterious CLKOUT2 pin on P9 - they do not recommend using the output because it has an unspecified jitter, although the BBB uses CLKOUT1 as an input for the HDMI Framer. Couple questions - what output does one see on CLKOUT2? (I don’t have a high bandwidth DSO handy). I’m wondering if I should bother with the clock, or just use the on chip clock found on the peripheral IC.
Then I thought I should set up a PWM at 50% duty as a clock source. However, I’m unable to locate the maximum PWM frequency that can be set up. Any pointers? Any clever ideas?
Cheers,
K
My suggestion is that you consider an external oscillator due to the issue as described in the TRM. But, you copuld also design it such that with a resisotr swap, you could use either one. I am not sure how good the CLKOUT2 frequency is at 16MHz. A lot of this depends on what exactly your application s and how you are using it.
Gerald
I was thinking about using an I2S DAC such as a cheap TDA1543 (9Mhz clock input max, could not find a MAX5556 around here which is OK with up to 25Mhz clock input). I want to be able to get no-so-high-end audio without the HDMI interface for an SDR project.
The “SPI1_SCLK - P9_31 - Bit clock” pin on the expansion board is CLKOUT1, which is used for the HDMI Framer Processor. It’s at 24.576MHz, and it would be good for a MAX5556 without a divider for my purpose.
This CLKOUT1 is constantly on (I see it on my DSO right now, since it’s a cheap 25Mhz one, the pulses look almost like sine waves), so I think it could be used with a frequency divider just as they do with the SN74AUC1G74 to provide the 12MHz clock signal for the TDA199988.
Regards,
Emrah