Weird problem on rs232 vs USB-serial...

[Joel Sherrill]

mike wrote:
> Thanks Steven,
>
> One more addition is:
>
> - if I use 'grmon' to connect to the DSU port, then load the same app 
> with grmon and run,
> I can see outputs coming out of the COM1 port.
>
> - it was when I used the onboard bootrom to load the app to ram, then 
> jump to it that I didn't
> see any outputs on COM1 port. Again, when it's connected to 
> USB<->serial, the outputs
> came out fine, with the same app.
Could the flow control settings be wrong in the comm application when 
using the ttys0?
I recall that minicom on unix defaults to HW flow control on.
> Anything else I need to look? Thanks again.
>  
>  -mike-
>
>
>
>
> Steven Grunza wrote:
>> My first suggestion would be to use a Voltmeter to measure the Voltage
>> on the PC's COM1.  Assuming a DB9 connection you should see -5V or more
>> between pins 3 and 5.  If you have a DB25 then check between pins 2 and
>> 7.  
>>
>> Back in the old days (before Maxim's MAX232 and similar chips) it wasn't
>> unusual for a cheap RS-232 interface to "steal" negative Voltage power
>> from the other end of the connection.  This usually worked well unless
>> the data rate was too high or the other end was also trying to "steal"
>> negative Voltage power.  I know of some Tandy machines that used this
>> trick.
>>
>> The USB part probably uses either a Maxim or other vendor's RS-232
>> interface powered from the 5V available on the USB interface.
>>
>>
>>
>> That's it for my USD 0.02
>>
>>
>>
>>   
>>> -----Original Message-----
>>> From: rtems-users-bounces at rtems.org 
>>> [mailto:rtems-users-bounces at rtems.org] On Behalf Of mike
>>> Sent: Monday, February 23, 2009 2:03 PM
>>> To: RTEMS Users
>>> Subject: Weird problem on rs232 vs USB-serial...
>>>
>>> Hi all,
>>>
>>> We have a Leon2-based board using the RTEMS leon2 BSP. The 
>>> host is x86 running CentOS 2.6.
>>> With a simple application that outputs to /dev/console for 
>>> stdio (printf):
>>>
>>> - with the board connected directly to COM1 of the host, no 
>>> output is seen
>>>
>>> - with the board connected to a USB<->serial adapter 
>>> (Keyspan), outputs and inputs were fine
>>>
>>> * This is with the same app initializing the UART to 38400, 
>>> 8N1, no flow control.
>>> * On the host, we just use 'minicom' set for 38400, 8N1, no 
>>> flow control
>>>    (/dev/ttyS1 in the 1st case and /dev/ttyUSB0 in the 2nd case)
>>>
>>> What could possibly be the cause?
>>> Thanks for any comments/pointers.
>>> -mike-
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> rtems-users mailing list
>>> rtems-users at rtems.com
>>> http://rtems.rtems.org/mailman/listinfo/rtems-users
>>>
>>>     
>>
>>
>>   
>


-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
   Support Available             (256) 722-9985