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Topic: NewSoftSerial Duemilanove - baud rates? (Read 5194 times) previous topic - next topic


Well I simplified it by just using the sketches in reply #8. Simply sending the messages out straight from the arduino. Mikal has confirmed that there doesn't appear to be anything wrong with the logic - "Logically this seems ok. Are all devices grounded? All operating at the correct voltage? There isn't any RS-232 anywhere, is there?"

However I suppose there is RS232 by way of the level shifter..

I'm not sure that there is much left to try, I'm sure the LCD device itself is fine because it works through the dedicated UART port through the level shifter just fine, and through the PL2303.

The only other thing to try is a .22uf cap in place of C1 of the charge pump required for the Max 3323 which is specified in their datasheet but this is not what is shown in the arduino rs232 tutorial - http://www.arduino.cc/en/Tutorial/ArduinoSoftwareRS232

I'm not convinced this would actually achieve any different results though as the existing circuit (wired the arduino rs232 tutorial way) works through the UART pins.


Sep 01, 2010, 11:36 pm Last Edit: Sep 01, 2010, 11:37 pm by mpeuser Reason: 1
You never proved how you wired the MAX... especially the pins 11,12,13 have to be HIGH, as this is a very specialized chip (and should never have been used as an tutorial example)!

I feel still a little bit uneasy about the +/- 6 V... It shpould vave been 10...

But as you said, it works with HardwareSerial....

It is not worth posting a screenshot of the oscillogram. I ran HardwareSerial and NewSoftwareSerial in parallal an the signals were highly correlated. SoftwareSerial - as posted -lost a little bit, 20us from stop bit to stop bit = 20us/1ms = 2%. This is inside the tolerance....


I have also now wired exactly as the 'Typical Operating Circuit', under the '±15kV ESD-Protected, RS-232 Transceivers for Multidrop Applications' section of the chip manufacturers datasheet: http://datasheets.maxim-ic.com/en/ds/MAX3322E-MAX3323E.pdf


1 - C1+
2 - C3+ (- to gnd)
3 - C1-
4 - C2+
5 - C2-
6 - C4+ (- to gnd)
7 - Connected to the serial of the Milford LCD
8 -
9 -
10 -
11 - 5v
12 - 5v
13 - 5v
14 - 5v
15 - gnd
16 - 5v

I'm assuming now it can only be the NSS timings or an extremely sensitive LCD unit..?


Sep 14, 2010, 06:33 am Last Edit: Sep 14, 2010, 06:34 am by mpeuser Reason: 1
Still working on your problem?

In the meantime there had been two more issues with NSS
(1) The receive via NSS shows a garbled character from time to time (should have not so much to do with your issue)

(2) The transmission or receive of a character by NSS happens uninterruptable. This means that a character to be received through hardware serial might get lost, if the bit rate of NSS is slow. So against the common feeling the NSS should work better the higher its bit rate. Especially the bit rate for hardware serial should be lower or at least thesame to avoid drop outs here.

Alas, all this can hardly have to do with your issue, as you reflect all incomming characters correctly back to the PC.... Though it might beworth an experiment to set the PC (!) connection down to 4800 baud

I have again looked through the NSS code, but no obvious mistakes there....

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