Weird problem on rs232 vs USB-serial...

[mike]

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.
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-
>>
>>
>>
>>
>>
>>
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>>
>>     
>
>
>   

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