Subject: Re: High serial port (output) speeds
To: der Mouse <mouse@Rodents.Montreal.QC.CA>
From: Jukka Marin <>
List: port-sparc
Date: 10/22/1999 08:25:20
On Thu, Oct 21, 1999 at 11:20:26PM -0400, der Mouse wrote:
> I think I know why the zs chips are normally run with a X16 clock
> divisor.  But is there any reason why they shouldn't run X1 if userland
> requests a baudrate that can be achieved that way but not with X16?

Many UART chips use the 16x clock to sample the RxD pin multiple times
for every bit, then they use a majority algorithm to determine the final
state of the bit (in case all samples don't agree).  I don't know if
this is what the zs chip is doing with the 16x clock - probably yes.

In a quiet environment with good cables and UARTs and transceivers it
shouldn't really matter - but if there's noise and/or voltage spikes,
you'll get transmission errors easier with the 1x sampling method
(although I have used it successfully when creating bit-banged serial