Re: [Sdcc-user] Getting started with C8051F120 problem
On 29.12.2016 23:16, Maarten Brock wrote: > > These values get you a 453 baudrate: > 24.5MHz / 8 / (256-45) / 32 = 453 > > 300 baud is really low and impossible to achieve with T1 in 8-bit > autoreload. Most USB-UARTs even have this as their lower level limit. The 43 in the posted example was wrong. But the timer uses a prescaled sysclk giving another division by 12, thus I can do: 24.5 * 100 / 8 / 12 / (256-229) / 32 = 295.38 when running at 3.0625 Mhz and 24.5 * 100 / 12 / (256-43) / 32 = 299.54 when running at 24.5 Mhz. The former didn't work for me (it is off from 300 by 1.54%), but the latter did (off from 300 by 0.15%). Philipp -- Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot ___ Sdcc-user mailing list Sdcc-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/sdcc-user
Re: [Sdcc-user] Getting started with C8051F120 problem
> On 29.12.2016 23:16, Maarten Brock wrote: >> >> These values get you a 453 baudrate: >> 24.5MHz / 8 / (256-45) / 32 = 453 >> >> 300 baud is really low and impossible to achieve with T1 in 8-bit >> autoreload. Most USB-UARTs even have this as their lower level limit. > > > > The 43 in the posted example was wrong. But the timer uses a prescaled > sysclk giving another division by 12, You're right. I forgot about CKCON and its default. > thus I can do: > > 24.5 * 100 / 8 / 12 / (256-229) / 32 = 295.38 > > when running at 3.0625 Mhz and > > 24.5 * 100 / 12 / (256-43) / 32 = 299.54 > > when running at 24.5 Mhz. The former didn't work for me (it is off from > 300 by 1.54%), but the latter did (off from 300 by 0.15%). > > Philipp In general for a UART 1.5% should be good enough. Anything below 2.5% should work. But you must take the tolerance on the internal oscillator into account as well. And then you get 1.5% + 2% = 3.5% which might fail. It also depends on the accuracy of the other side. Maarten -- Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot ___ Sdcc-user mailing list Sdcc-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/sdcc-user
