receiving incorrect data from max3221cp

swati arora

Other Parts Discussed in Thread: MAX232

hello i am using lm4f132 and i want to communicate it with max3221cp. the forceoff pin of my max3221cp is gpio high and forceon pin is pulled low for using auto powerdown mode.and this is connected with the db9 connector so that i can transmit data to my pc and receive from it.

the problem i am facing is :

i am transmitting data through microcontroller and receiving at the max ic and this ic will send this data to pc application terminal using db9 connector,here i am not getting the correct data e.g. if i am sending character 'a' at the pc i am receiving 'B'. and when i am sending 'd' i am getting ! .and same problem occures when i am trying to send the data from terminal and recived at microcontroller.

it will receive the data but the "incorrect data"

please help me out how to get back from this problem.

over 12 years ago

0 Gautam Iyer over 12 years ago

Guru 192875 points

Hi Swati,

Did you try using Hex values for characters and numbers?

Check on this link: http://www.asciitable.com/

Regards,

Gautam

0 swati arora over 12 years ago in reply to Gautam Iyer

Intellectual 770 points

yes ofcourse i have checked their hex values also but these are incorrect.

i am getting "B"=42 even when i am sending 'a'.

0 swati arora over 12 years ago in reply to swati arora

Intellectual 770 points

and when i was sending 0x61 in the place of a as u said in that case i was getting ox00.

0 Gautam Iyer over 12 years ago in reply to swati arora

Guru 192875 points

Thats very weird Swati! Anyways, did you try replacing max3221cp chip? (Personally I feel, the max232 chip would be fine)

Regards,

Gautam

0 swati arora over 12 years ago in reply to Gautam Iyer

Intellectual 770 points

no i dint replace the ic..but i do not think so there should be any problem..

can you tell me that when controller will transmit data to the max ic ,data will be received at the Din pin of ic and ic will transmit the same data through Dout pin to any connector which we are using..

right???

0 Gautam Iyer over 12 years ago in reply to swati arora

Guru 192875 points

Right, but this is how you can eliminate your doubts:

1. Check with the loopback connections; keep transmitting some data continuously(Connect Rx to Tx of your controller and check their register values on watch window) - This will eliminate your doubts on controller data transmission.

2. If the above seem to be working fine, next comes the max232 ic issue.

Regards,

Gautam

0 swati arora over 12 years ago in reply to Gautam Iyer

Intellectual 770 points

i have checked this.

controller is working fine.

0 Gautam Iyer over 12 years ago in reply to swati arora

Guru 192875 points

So the hex value that you transmit is properly viewed in Rx register on CCS watch window. Then, max ic seems to be generating an error (!?)

Are the hardware connections fine?

0 swati arora over 12 years ago in reply to Gautam Iyer

Intellectual 770 points

sorry i dint check the register value that time..

now i have made connections on the board and can not do again the loopback test..

infact when i connected the db9 rx and tx pin means trying to loopback on ic.

but did not get any value

0 swati arora over 12 years ago in reply to swati arora

Intellectual 770 points

hey when i tried 'a' i got 'B'=42

and when i tried '0x61' i got 'B'=42

means now i have a fix problem.

its really strange how can i get the incorrect value???how a would be convert to "B"

0 Gautam Iyer over 12 years ago in reply to swati arora

Guru 192875 points

First of all, your loopback test should work. There's a question mark over there itself whether its at the controller end or after max232. Secondly, if data is getting altered while getting transmitted as you say then there seems to occur some kind of data corruption. I hope the baud rate matches exactly.

Regards,

Gautam

0 Ron Michallick over 12 years ago in reply to Gautam Iyer

TI__Guru**** 164976 points

Swati,

I suspect that baud rate may be a factor. If the micro controller RS232 packet code is not proven, then may other possibilities arise. Can you look at the data with an oscilloscope?

0 swati arora over 12 years ago in reply to Ron Michallick

Intellectual 770 points

hello,

thanks for your support,

the problem has been solved,it was really a stupid mistake,

i thought external osc is of 8 mhz but it was of 16 mhz..

now everything is working properly..thanks again!!

0 Gautam Iyer over 12 years ago in reply to swati arora

Guru 192875 points

Good to know. Congrats.

Cheers,

Gautam

0 swati arora over 12 years ago in reply to Gautam Iyer

Intellectual 770 points

thank you..:)

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receiving incorrect data from max3221cp