Hi guys,
Courtesy of my colleague Danny Scott, I have a functioning USB 2 build running on my hardware, but I've had to up the clock frequency from 8MHz to 48MHz. I'm only using it as a replacement for a UART for serial comms, and I'd be happy using USB 1.1 if I could lower the processor clock back down to the original 8MHz again.
Can anyone point me at any documentation that describes using Jerry Messina's USB library at lower clock speeds for USB 1.1 ?
Best regards,
Nigel
USB 1.x
Moderators: David Barker, Jerry Messina
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Re: USB 1.x
Nigel,
On most of the chips you need to get 48MHz (or some multiple) into the USB engine. You can usually run the cpu at a different frequency if you like, but how you do that depends on the device. There's usually a different clock tree for the uC. One thing... you need to respond to enumeration requests at a pretty quick pace (~100us), otherwise you'll have problems.
You need to be a USB full-speed device to be spec compliant with the CDC class, so while you can sometimes get low-speed to work it's not a good idea.
On most of the chips you need to get 48MHz (or some multiple) into the USB engine. You can usually run the cpu at a different frequency if you like, but how you do that depends on the device. There's usually a different clock tree for the uC. One thing... you need to respond to enumeration requests at a pretty quick pace (~100us), otherwise you'll have problems.
You need to be a USB full-speed device to be spec compliant with the CDC class, so while you can sometimes get low-speed to work it's not a good idea.
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Re: USB 1.x
Jerry,
Many thanks, I will investigate.
Nigel
Many thanks, I will investigate.
Nigel
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- Swordfish Developer
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Re: USB 1.x
I meant to add... I think Danny was using the 67J94, if so look at the CPDIV[1:0] bits in OSCCON4.