# Forum: ARM programming with GCC/GNU tools Olimex power supply

 Author: Abe Abe (olimex) Posted on: 2008-08-07 14:37

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Hi,

I'm using Olimex-board LPC-P2138 and programming it with Rowley Cross
studio 1.9.
I disconnected ARM-USB-OCD connector and tried to use an external power
supply (i just disconnected power supply, not JTAG) but cross studio
doesn't recognise the target. Even when i download program to target and
then connect an external power supply, program doesn't work. Where can
be the problem?How to use an external power supply?

Thanks for answers!

 Author: Martin Thomas (mthomas) (Moderator) Posted on: 2008-08-09 14:15

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Abe Abe wrote:
> Hi,
>
> I'm using Olimex-board LPC-P2138 and programming it with Rowley Cross
> studio 1.9.
> I disconnected ARM-USB-OCD connector and tried to use an external power
> supply (i just disconnected power supply, not JTAG) but cross studio
> doesn't recognise the target. Even when i download program to target and
> then connect an external power supply, program doesn't work. Where can
> be the problem?How to use an external power supply?

I do not own this board and do not own the Olimex ARM-USB-OCD so take it
for what it's worth: Did everything work as expeced while you have used
the power-supply from the ARM-USB-OCD connected to the board's
power-jack? Than you unplugged the power-supply from the USB-OCD and
connected another power-supply? Did you connect the other supply to the
power-jack or did you use a 3,3V supply and connected it "behind" the
regulator (VR1)? If yes, is the external supply stable?

Some tests: disconnect the JTAG-device, connect you external
power-supply and measure the voltage (i.e. at Pins 2 and 4 of the
JTAG-connector, see schematic). Verify that the voltage is around 3.3V.
Compare this with voltage measured when the ARM-USB-OCD is used as
power-source. Check if there is a common GND.

If Cross-Studio detects the target later even with the external supply
but the firmware does not run after power-toogle check if the firmware
gets loaded into the controller's flash-memory (not just in RAM).

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