Extra UARTs

bretesq · Joined: 07 Feb 2006 Posts: 16

Hi guys,

I'm doing a personal project now where I'd like to setup a "Serial" server for my 4 servers I have running in a datacenter. I have got the ethernet working with the enc28j60 chip and the tcp/ip stack from microchip/ccs. What hardware UART chip would you recommend for me to use to gain the 4+ serial devices I have. I'd like them to be able to transfer at least at a rate of 38400 bps each. I don't think using the software UART within a PIC18 chip would be that efficient. Anyone have some insight?

Thanks!

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

I have implemented two software UART and a hardware UART on a PIC18F452 running at 40MHz. Both software UARTs were running at 115Kbps.

Maxim make an SPI connected UART but I have not yet implemented it.
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

newguy · Joined: 24 Jun 2004 Posts: 1908

sebdey · Joined: 11 Sep 2003 Posts: 17 Location: Switzerland

If you can use the SPI port, try the MAX3100 from Maxim's:

(http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1731)

We are using it in one of our products, no problems with it...

bretesq · Joined: 07 Feb 2006 Posts: 16

j_s_connell · Joined: 02 Feb 2004 Posts: 17

The spi bus can be shared with the enc28j60, as long as you have an extra CS (chip select line) for the uart chip. People using the enc28j60 often share the spi bus with an sd/mmc card (to store web pages). See this post:

http://www.ccsinfo.com/forum/viewtopic.php?t=27330

for some reference designs where the enc28j60 is shared on the spi bus.

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

I forgot to add, I use a single timer for the transmit bit timing servicing multiple sw uarts. It is tricky impementing the software UARTs transmit logic because all paths through the transmit interrupt handler state machine for a given comm port must be the same otherwise jitter (and therefore the possibility or errors) will be introduced for the remaining comm ports lower down in the chain of the transmit bit interrupt handler. My interrupt handler is implemented in assember and it took me a full day of tuning to ensure this condition was met.
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands