PIC <--> Sensor RS232 Communications...Please Help

[weg22]

Hello all,

I recently purchased an IMU from Microstrain that tx and rx data serially. When connecting the sensor to the PC and pinging it (thru hyperterminal) for the device serial # (using the command BYTE 241 as defined by Microstrain), it sends back 5 BYTES which correspond to:

BYTE1: 241 (command that I sent to the IMU)
BYTE2: 6 (MSB of the serial number)
BYTE3: 251 (LSB of the serial number)
BYTE4: xxx (MSB of checksum -- used for sanity check...not important)
BYTE5: xxx (LSB of checksum -- used for sanity check...not important)

I'd like to get the same response when pinging the sensor using my PIC micro. I am using a PIC 16Fxxx and am trying to use the getc() command to receive this data packet. But this is not working for some reason (the format of my code is shown below). I get a different number every single time -- maybe my timing is off? The default baud rate for the sensor is 38400. Any suggestions would be much appreciated.

#use rs232(baud=38400,xmit=pin_B1,rcv=pin_B0)

// main starts here...
int sn1, sn2, sn3, sn4, sn5; // define 5 BYTES

putc(241);

while(!kbhit())
{
sn1 = getc(); // get 1st BYTE
sn2 = getc(); // get 2nd BYTE
sn3 = getc(); // get 3rd BYTE
sn4 = getc(); // get 4th BYTE
sn5 = getc(); // get 5th BYTE
}

Thanks in advance,
-Bill

[Ttelmah]

Your while loop is wrong/silly...
getc, will wait for a character if no character is present.
Just use the getc commands without the while. As it stands, it'll only enter your while loop, if no character is 'waiting' following the command. You should probably clear the buffer first. So:

[weg22]

Thanks for the reply. I tried both with and without the while loop. I also tried flushing the buffer as you suggested, but I am still getting unexpected values back from the sensor.

I am using a 10 MHz crystal and a MAX233 converter chip. I'm assuming you mean are there common grounds between the PIC and MAX...the answer is yes.

Any more help you (or anyone else) could provide is greatly appreciated.

Thanks,
-Bill

[PCM programmer]

[Ttelmah]

What about the grounds between the Max, and the sensor?.
At 10MHz, the error on the baud rate, should be 1.73%, which ought not to be a problem. What are the actual values you are seeing, compared to the expected values (after all you know what the first byte is meant to be). It may be possible to see what is going wrong from the values received.

Best Wishes

[Guest]

Well, let me start over by describing the setup I have in more detail. On the PIC, I am using pins A0,A1 to tx/rcv RS232 commands to the MAX which is connected with the sensor. Then, to see what I get back from the IMU, I am using pins B0,B1 to tx/rcv RS232 commands to another MAX chip which is connected with the PC (this is so I can see the sensor response via hyperterminal). Before your last posting, I had the sensor powered through an AC adapter and the PIC circuit powered through a separate power supply.

After reading your last posting, I eliminated the AC adapter and am now powering everything on the same PS. However, I do not get any response this way. I went back to the old way (separate PS) and this is what characters I expect and what I actually get after sending the 241 command to the sensor:

Should get the following and do when I connect PC directly to sensor:
ñûì

With PIC, I got the following responses...all different:
gÎïÞŽ
nOgO
öžÎÏ
÷ççïç
î÷ïÇÎ
óçÞŸþ
ç–çç
gîæÇÏ
fççÇÏ
gçæÆÏ
gïçï

Here is my exact code in case you see something I might have missed.

[Guest]

Well, let me start over by describing the setup I have in more detail. On the PIC, I am using pins A0,A1 to tx/rcv RS232 commands to the MAX which is connected with the sensor. Then, to see what I get back from the IMU, I am using pins B0,B1 to tx/rcv RS232 commands to another MAX chip which is connected with the PC (this is so I can see the sensor response via hyperterminal). Before your last posting, I had the sensor powered through an AC adapter and the PIC circuit powered through a separate power supply.

After reading your last posting, I eliminated the AC adapter and am now powering everything on the same PS. However, I do not get any response this way. I went back to the old way (separate PS) and this is what characters I expect and what I actually get after sending the 241 command to the sensor:

Should get the following and do when I connect PC directly to sensor:
ñûì

With PIC, I got the following responses...all different:
gÎïÞŽ
nOgO
öžÎÏ
÷ççïç
î÷ïÇÎ
óçÞŸþ
ç–çç
gîæÇÏ
fççÇÏ
gçæÆÏ
gïçï

Here is my exact code in case you see something I might have missed.

[PCM programmer]

What's your version of the compiler ?
This will be a number like 2.734, or 3.191, or 3.225, etc.
You can see it at the top of the .LST file which is generated
when you compile a file successfully.

Also please register (and set your preferences to auto-login)
so that when you get a double post you delete one of them.

[weg22]

I have version 3.143

[Ttelmah]

Post the characters in Hex, rather than as ASCII.
You still have not confirmed that the ground connection is made between the Max at the PIC, and the sensor. Though it probably is, it'd be nice to have this 'in writing'.
Now, the big questionable thing here, is the accuracy of software RS232. 3.143, is fairly old, and there have been problems with some versions in the past with the software RS232 timings. It might be this.

Best Wishes

[Humberto]

Replace:

[PCM programmer]

The first thing I would do is to prove that the PIC can transmit
correctly to your PC. Disconnect the IMU from the PIC board,
and connect the PIC board to the PC. Then try a program like this:

[weg22]

Yes, I've done this already. The PIC can successfully communicate to the PC and the PC to the PIC. That is not the issue. When displaying the data in HEX format, I get the following (after 3 loop iterations):

GM*;O+KO/;w´=W<
YÛ^Û÷4ß–6ßv>û
ÓMh=K:[W6ntßtþ

Pretty crazy, huh? Is there a possibility that the baud rate of the sensor (38400) is too fast for the PIC with a 10MHz oscillator? The sensor also has a 19200 baud rate which I am going to try now...

Oh yeah, my grounds are connected.

[PCM programmer]

Try the lower baud rate, and if it doesn't work then try adjusting
the baud rate in the #use rs232 statements. Try 39000 and then
try 37000. Those values will cause the delay loop in the soft UART
to change by a count of 1 in either direction, from the value used
for 38400 baud.

[Mark]