Not expected values...

Projects Programming
1

I ve got a little problem, i m working with a serial device with a known protocol and using 19200 8n1, i use a teensy set up as a virtual com port device so i can use serial terminal or real term to read the data coming from the device. But the values i got don't match what i expect. The packet length are good, i need 5 bytes packet, but the values are messed up.

Exemple : I should have that type of value (decimal) : 241 ( hook byte ), 63(values can go from 0 to 127),13 (values can go from 4 to 22) ,63 ( can go 0 to 127 ) and 10 ( can go 4 to 17 ).

But what i get i an hex which looks like this : 87 67 F5 22 00 in decimal : 135,103,245,34,0 so obviously not really what i expect...
What can mess up my data packet like this ?
Any help is welcome.

2

i m working with a serial device with a known protocol and using 19200 8n1

TTL or RS232?
If the latter, what is doing the level conversion and inversion?

3

that's the tricky part, the device is labelled rs232 but it output 5v ttl level signals.

4

That's OK - if the device is RS232, the voltages could be +/- 5V (NOT TTL), but inverted wrt true TTL.

5

So i should convert them somehow ? Heres the sketch i use to monitor thing on REALTERM.

//  echo on TX (pin1) from RX software (pin 2)

#include <NewSoftSerial.h>


NewSoftSerial tabletteSerial(2, 3); 

void setup()  
{
  Serial.begin(19200);         Serial.println("Bonjour");

  tabletteSerial.begin(19200);
}

void loop()                     
{
  if (tabletteSerial.available()) {
      Serial.print((char)tabletteSerial.read());
  }
}
6

First mention of softwareserial.
You could try the "invert" optional parameter to "begin"

NewSoftSerial myInvertedConn(7, 5, true); // this device uses inverted signaling
NewSoftSerial myGPS(3, 2); // this one doesn't

7

i ve done it, as expect i ve got new sets of HEX values, but still no sign of the value expected, and now in realterm i ve got a lot of "break" and "error" while receiving the packets....

8

OTher way to invert is to do

Serial.print((char)(255 - tabletteSerial.read()));

Do you have a datasheet link of the device in question ?

9

same, new values but still no signs of the expected ones. And a lot of break and error.
For the datasheet, there is one, but not really filled with infos, but there is a lot of stuff on the website, what should i look for ?
( its the same tablet device i started a thread about in device hacking : SignatureGem 4x5 Signature Pad - Topaz Systems ).

10

OTher way to invert is to do

Serial.print((char)(255 - tabletteSerial.read()));

That's assuming that the start bit was recognised correctly.

11

ok progressions :slight_smile:
i modified the sketch using the inverted "(true)" parameters, i ve got errors but i manage to correct it because i forgot to set all the serial the soft one and the hard one to 19200.
I know have the expected first bytes which are the status of the stylus. And they re correct. But the following bytes are still not what i expect, the values are too high. and i have a packet of 6 bytes instead of 5 ... i presume there is a separator or stop byte in this ?
i m wondering if it's not a "parity bit" problem... how could i change the parity in newsoftserial ?

12

I just had a quick look at the library, and after the eight data bits, the receiver simply skips the stop bit, and then presumably re-arms ready for the next character.
I guess you could slip in an extra " tunedDelay(_rx_delay_stopbit)" to skip parity too.

13

i tried but have some not declared errors, should i add this delay in the void loop when serial.available ? or in the setup ?

echorxsoftpin2:21: error: '_rx_delay_stopbit' was not declared in this scope
echorxsoftpin2:21: error: 'tunedDelay' was not declared in this scope

14

i tried but have some not declared errors, should i add this delay in the void loop when serial.available ? or in the setup ?

Neither; in the library.
You may want to add a "parity" flag to the "begin" method.

15

Ok so i should open newsoftserial.h and edit tuneddelay to 1 ?
And then flag the parity in the begin like serial.Begin(19200, N) ?

16

ok in the library i see :
// skip the stop bit

tunedDelay(_rx_delay_stopbit);
DebugPulse(_DEBUG_PIN2, 1);

so i should add
// skip the parity bit
tunedDelay(_rx_delay_paritybit);
DebugPulse(_DEBUG_PIN2,1);

?

17

Yes, I think that's where I'd put it, but make it conditional upon the parity flag (for guidance, look at the "inverse_logic" flag, which I failed to notice is in the constructor, not the "begin" method)

18

ok i ve noticed the inverse_logic flag, but i thing it exceed my programming competence, i have no idea what should i do to it, and make the good conditionnal value for my extra stop bit..

19

ok, i ve added the extra skip parity bit

without making conditionnal ( because i still don't know how to do it )
But i can say that now my 5 bytes packet are looking good.
You helped me a lot :slight_smile: thanks

first, third and fitth byte, are getting me the values i expect, not sure about second and forth thought... but seems impossible that i can get some bytes right and the other wrong ? or is it ?

20

How "wrong" are they?
Even if there's a severe speed mismatch, the receiver should re-sync at the start of each character, so any problems should affect all characters equally - the receiver has no concept of packets.