UART problem when link and MCU seperated

lpcware · ‎06-15-2016

Content originally posted in LPCWare by serhangul on Tue Mar 27 07:22:14 MST 2012
Hi,

We have broken the connection between the link and the MCU and we supply power externally (3.1 V) to the MCU. In this case, the UART does not function properly for some reason. Before we had broken the link, we had been getting proper data out of UART, but now with external power supply, it is not functioning.
We are sure that the MCU is running properly, we tested it with a simple LED on-off program.
What might be the cause of this problem and how can we solve it?

Thank you,

Serhan

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Rob65 on Wed Mar 28 12:59:51 MST 2012

Quote: serhangul

Also we tried this, we supplied upto 3.55V to the VIO_3V3X pin ( and nothing to EXT_POWX pin), but we still could not get a proper uart functioning. However, as we have increased the supply voltage (from 3.1V to 3.55V), the data we received on the computer from uart became "more" correct. With low voltages it is nothing related to what we are sending but with high voltages it resembles what we are sending.

I don't remember if it was with Polux but we've seen a similar problem before:
a bad ground connection between the "serial to usb converter" and the LPCXpresso board.
With the LPC- Link still connected, the board got it's ground from the PC's USB and being the same ground as the converted cable there was no problem.
As soon as the LPC module was powered using an external power supply, the ground connection with the converter was missing ...

Check the connections between the usb-serial module and your LPCXpresso board.

Just power the board with a proper 3.3V signal - there is absolutely no need to use strange voltages like 3.1 or 3.55V.
When in doubt, always check the datasheets and the schematics.
And measure your data with an oscilloscope or logic analyzer to be sure that what you think is happening indeed does happen.

Regards,[INDENT]Rob
[/INDENT]

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Polux rsv on Wed Mar 28 06:14:02 MST 2012
Check all the ground connections. Is your serial converter also connected to GND ?

Angelo

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Tue Mar 27 10:08:20 MST 2012
FYI:

My separated original LPC1769 target board is transmitting and receiving with voltages >[COLOR=Red] 2.2V[/COLOR] (at VIO_3V3X / GND)

without problems via UART0 and TTL to USB converter (FTDI chip inside) :eek:

Terminal program is Tera Term :)

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Tue Mar 27 09:35:58 MST 2012
Are you sure that your 'serial to usb converter' is able to work with 3.3V?

Are you sure your terminal program (?) isn't kidding you?

lpcware · ‎06-15-2016

Content originally posted in LPCWare by serhangul on Tue Mar 27 09:28:31 MST 2012
Hi,

Quote: Zero

voltage regulator is placed on LPC-Link and can be powered via EXT_POWX. This voltage regulator is supplying your target board via VIO_3V3X :eek:

So if you want to power your target board via 5V you have to connect EXT_POWX and VIO_3V3X at debug connector J4.

As you have told, we have supplied 5V to the EXT_POWX pin, connected VIO_3V3X, EXT_POWX and GND pins on the jumper J4. We saw 3.13V on the VIO_3V3x pin again. Then we tested the uart and it did not function again.

Quote: Zero

You should supply at least 3.3V to avoid that your 'serial to usb converter' is failing :rolleyes:

Also we tried this, we supplied upto 3.55V to the VIO_3V3X pin ( and nothing to EXT_POWX pin), but we still could not get a proper uart functioning. However, as we have increased the supply voltage (from 3.1V to 3.55V), the data we received on the computer from uart became "more" correct. With low voltages it is nothing related to what we are sending but with high voltages it resembles what we are sending.

Thanks again.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Tue Mar 27 09:03:31 MST 2012
As explained in schematic,

http://www.embeddedartists.com/sites/default/files/docs/schematics/LPCXpressoLPC1769revB.pdf

voltage regulator is placed on LPC-Link and can be powered via EXT_POWX. This voltage regulator is supplying your target board via VIO_3V3X :eek:

So if you want to power your target board via 5V you have to connect EXT_POWX and VIO_3V3X at debug connector J4.

EXT_POWX isn't connected to anything on target board :rolleyes:

You are measuring less than 5V (with USB connected) because there are diodes included.

You should supply at least 3.3V to avoid that your 'serial to usb converter' is failing :rolleyes:

lpcware · ‎06-15-2016

Content originally posted in LPCWare by serhangul on Tue Mar 27 08:53:43 MST 2012
Hi,

Quote: Zero
Perhaps you can disclose what LPCXpresso you have broken, what's connected to UART and why you don't supply 3.3V :rolleyes:

The board is LPC1769.
We have measured the voltage when the Link was connected on the pin and found 3.1V.
The uart is connected to a serial to usb converter, and goes to usb into the computer. We are using the system to read values from the ADC and send them to the computer via uart and usb.

Quote: Polux rsv
And where on the board you supply the 3.1V ? :D
Angelo

On the 28th pin, VIO_3V3X.

New data: also we have only remade the 5V and GND connections btw the link and the MCU and plugged the link into computer via its usb cable and in this case the uart functioned properly. We thought that there was some kind of chip that needed 5V to function on the target side so we have again discarded the link side; disconnected the connetions btw two sides and unplugged the usb cable of link but provided an external 5V to the 2nd pin on the board (EXT_POWX). In this case it did not function either. So is there also something on the link side that needs 5V for the uart to function????(this seems silly but still...)
Also when we give 5V via usb (via link side) we see 4.5V at EXT_POWX pin, but when we supply 5V directly t that pin we see 5V(or what we give).

Thanks for your help and interest.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Polux rsv on Tue Mar 27 08:05:45 MST 2012
And where on the board you supply the 3.1V ? :D

Angelo

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Ex-Zero on Tue Mar 27 07:44:46 MST 2012

Quote: serhangul
What might be the cause of this problem and how can we solve it?

Perhaps you can disclose what LPCXpresso you have broken, what's connected to UART and why you don't supply 3.3V :rolleyes: