[GreenKeys] RS232 to TTY Loop Boards

[epvgk at limpoc.com]

On Mon, Feb 16, 2015 at 05:59:36PM -0500, Ralph Mowery wrote:
> 
> ----- Original Message ----- From: "Eric" <epvgk at limpoc.com>
> To: <greenkeys at mailman.qth.net>
> Sent: Monday, February 16, 2015 5:50 PM
> >Yes - that's the problem - on a lot of chips, the clock just can't
> >be programmed to go that slow. For instance on the chip I tried last,
> >you need to have the CPU clock at 16mhz for the USB bus to work right,
> >but the serial UART divisors can't be set high enough to divide this
> >down to 45 baud.
> 
> I am not familiar with the chips you are using, but couldn't a UART
> type chip be fed wth a differant than standard crystal to get to the
> lower clock frequency it needs ?
> Maybe they are built into the computer and can't beclocked by a
> seperate crystal.

The chips I'm talking about are integrated system-on-chip type setups
where the uart is built into and clocked from the same clock as the
CPU and the USB subsystem, so that's not an issue. On some ARM-based
systems-on-chip, there is much more flexible (and confusing!) clock
configuration where you can enable internal PLLs to have different
integrated peripherals clocked at different speeds, which is how I got
one of them to do 45 baud serial while the CPU was running at 48 mhz. 

eric

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