Lpc2000

I have had problems with USB serial interfaces. The utility works 
flawlessly at 115.2K on my desktop but can be a dog on some types of 
serial ports. I also had a PCMCIA serial card on my notebook that worked 
fine with TeraTerm yet would give me problems when I tried to use the 
Flash utility. You didn't say what i/f or o/s you were using. Check your 
settings, fiddle with the buffer thresholds etc. I suspect the utility 
could handle the timeouts better. Don't forget to decouple the MAX.

RS-232!
IMO, the lower the drive voltage the better, far less for the drivers to 
slew through at high data rates. I much prefer an interface using 0 to 
+3-5V drive through a biased 422 chip. They don't have all the symmetry 
problems etc that come with the standard drivers. Nobody would think of  
putting +/- voltage drivers on an I2C or SPI bus just to drive it a few 
meters, would they?. Makes even less sense when you run a mere few 
meters to your PC at a snail's pace of 115.2K or less into what is a 
unipolar receiver with a switching threshold of 1.5V (check the specs!). 
Ahhhh, tradition! Professional gear will always need the +/- voltage for 
standards "compliance", but not necessarily for compatibility.

If you want to find out more about running "RS-232" at lower voltages, 
just read a Maxim app note. 
http://www.maxim-ic.com/appnotes.cfm/appnote_number/1834

Excepts:
"The old quad-receiver MC1489 has typical high and low receiver-input 
thresholds of 1.3V and 1.0V. The corresponding MAX3225E thresholds are 
specified at 1.5V and 1.2V, as are those of other interface parts. 
Therefore, the assumption that most positive thresholds are below 2.0V 
and negative thresholds above 0V allows an additional voltage drop on 
the cable."

"Most of today's RS-232 communications, however, require cables of less 
than three meters, e.g., connecting a cell phone or PDA cradle to a 
notebook computer, or a small PBX to a desktop PC. Those applications 
reside in the office or in the home, so noise immunity is not a big issue"

*Peter*

acetoel wrote:

>Yesterday I finished my LPC board. I used a MAX3232 CPE instead of the
>MAX232 that I used on the protoboard. The 3.3V and 1.8V regulators are
>working okey. And I have check the voltage on pin 6 and 2 of the
>MAX3232. In Pin 6 it was -5.5V and in pin 2 +5.5V. 
>
>When I open the Flash Utility and try to stablish a communication,
>everything works okey. I can set the baudrate at 9600bps and read the
>signature and the bootloader version. But when I tried to program the
>micro, it get's halted says "cannot communicate with board". So I slow
>down the baudrate to 4800, and the same happen. Until I get to 2400bps
>and it works okey, but I have to wait a long time...
>
>Is -5.5V and 5.5V a good voltage for the max? Or I will have to go
>back to the MAX232 (with 5V), whihc gave near -8V and +8V?
>