Anyone problems withe the RS232?

Hello guys,

i have some problems with the RS232 on the mini2440 board.
If i send something to the board i will only get garbage,
but if my mini2440 sends to my pc everything is almost okay.
Almost, because i need to connect the USB cable if i don´t connect
the USB cable i will get garbage, too. I think its a problem with the
shielding.....but if the USB and the seriall cable are connected i can
receive from the mini2440 without a probem, but i can not send something to
it.

Any advise?

b.t.w. i have tried 3 different PC´s and onboard and add on serial cards
and a usb to com converter. Only my old hp notbook can connect and i only
get some few transmition erros, but after all its untable too.

I have checked the signal from my RS232 cards with my osciloscope it looks
okay.

What bit rate do you use? Probably a lower bit rate solves your problem.
With a 12 MHz crystal on board it's hard to meet the higher bit rates with
full accuracy. If the mini2440 is 2% too fast and the PC 3 % too slow this
can garble the communication ... sometimes in one direction only depending
on the sampling algorithms of the UARTs.

HTH

One thing that could clear up any frequency tolerance issues would be to
get one mini2440 talking to another.  12MHz crystals would never be more
than, say 100ppm off frequency (0.01%).

You say the waveform looks O.K.  Proper levels? Start bit and data bits all
the correct length?  Can you actually measure how long a data bit is
(within +/-2%)? A general-purpose 'scope would not be able to do this.

Decided to fire the FriendlyArm up and test it myself.  Going to the serial
assistant in Qtopia, selecting /dev/tty/SAC0, 9600 baud, 8 bits and filling
up a few lines with the letter u and hitting the send button works in
Hyperterminal with the supplied null modem cable.

115200 baud works as well.

The letter u gives alternating highs and lows in the data stream, which
might make it easier to tell if you are on frequency or not.

The %error could vary with the baudrate chosen and a specific slow speed
may not have the lowest error.

Thx for response, i have noticed that the cable is straight trough...thats
stupid! i have used that cable to test my com ports today (i thougt it was
a crossover) and now i have 2 defect com ports.. lol..
but i have also noticed that i have experienced grounding problems... i
have solder a wire from gnd to the rs232 connectors shielding now it works
with the comport of my 2nd pc!

The next thing i do is changing the male connector against a female
connector and than i can use a normal cable for the connection. A cable
with 2 females is in most cases a null modem and its very hard to buy a
cable here with 2 females as a stright through.

My orginal cable is also damaged (contact problems)


b.t.w. the serial card was a 180Euro expensive industrie card (opto
insulated) , my stupidy makes me sad....

Finaly i got it!

I have soldered my own cable.

I have only use 3 pins:
RX, TX and Signal Ground. (PIN; 2,3,5)
as i have a opto insulated card i have not connected the
chassis ground, and bingo it works.

My RS232 card is still working i have spotted out that my cable was
faulty and therefor i had these transission errors..

CU Andreas

and thx for your help !

Great.  Have heard many stories about grounding on RS-232, but wasn't going
to suggest anything!

I encounter like that problem but I cant solved ,I also cant understand
your solution...Andreas can you help me ?

I have the same Problem with my mini2440, I connect to ttySAC2 with mini
connector, and have problems.

With the same connector, the same cable ...., in my mini6410 work with no
problems.

Who knows something to solve the problem....

Thanks.

hi,
anyone can plz help me out with my problem,
the problm is

when i connecting my mini2440 with my laptop using usb-serial cable, my
console is not showing clearly, iam getting some values inbetween like
this...
�root@FriendlyARM /]# 
�root@FriendlyARM /]# 
%��
ɥ��dlyARM /]� 
[root@Fri����I5�/5�
[r�o|@Frien�lyARM /]#�
[�oot@FriendlyARM /]# 
[r��
ɥ���l�ARM /]# 
�root@FrZY�I5�/]# 
[roo�@FriendlyARM /]# 
root�Fr�endlyARM /]# 
[ro�@Friendlyx�
               z�� �
                    [root�FriendlyARM /]# 
[root@Friendl^P
               z�� 
[root�Friendl^P�
                z�� 
[roo�@FriendlyP�
                z�� 
[roo�@FriendlyARM /]#�
+���
ɥ��&#6
5533;��I5�/]#

+���
ɥ��d�yARM /]#
C�[root@FriY���I5�/]# H�[root



what should i do to rectify this problem... iam using /dev/ttyUSB0... 
PLZ tell me solution....