Jean Rodrigues

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10 years, 6 months ago.

Bare LPC1768 mcu, how to wire it up?

Hi,

I've been playing with MCU's for a while (ATMEGA, ATTINY, XMEGA, Stellaris, LPCXpresso LPC1769 and FRM-025Z). I've relatively new to the ARM Cortex world. I can program and use my boards without any problem.

I just bought a LPC1768 (the bare mcu), soldered it in a LQFP100 prototype board and I am trying to figure out how to wire it up (vcc, ground, etc) and program it via ISP (using a standard USB-to-UART interface via PL2303).

I intend to use the internal oscillator at first, make things work together and then move to more advanced stuff.

What I did so far:

- Wired up the vcc and ground (no ref only vdd, ground and vddreg);

- Wired RX from PL2303 to pin 98;

- Wired TX from PL2303 to pin 99;

- RESET pin (17) to ground;

- ISP pin (53) to ground;

- RESET pin (17) to VCC (3.3);

And tried to use Flash Magic (ISP Mode). The message I get it "Operation Failed. Failed to autobaud - step 1" and now I'm stuck.

Could you help me figure out what is going on?

Thanks, Jean Rodrigues

4 Answers

Christian Lerche
10 years, 6 months ago.

First of: Do you pull RESET up after having it connected to GND? It's active low, meaning you have to connect it to GND and then 3.3V afterwards to startup the LPC1768.

You would probably like to put an 12 MHz crystal on the chip also. This will keep timing steady... And I'm not sure the LPC1768 will run without the crystal when compiling in the online compiler.

Lerche

Hi, Christian,

Yes, did pull RESET up. I'm not using any crystal, do I really need it? Or the internal one is enough for this?

I'm trying, at first, to read the device signature, but even this is failling...

Thanks, Jean Rodrigues

posted by Jean Rodrigues 22 Oct 2013

Try reversing RX / TX. If this doesn't help, Install a crystal, it should help.

posted by Christian Lerche 22 Oct 2013

I believe I tried to reverse RX/TX with no success. I'll take your sugestion of installing a crystal. I'll let you know if this works.

Thank you.

posted by Jean Rodrigues 22 Oct 2013
Neil Thiessen
10 years, 6 months ago.

I had this problem the other day while trying to program an LPC11U35 through a BT4.0 radio using Flash Magic. I could communicate with the LPC11U35 using Tera Term, but autobaud would always fail. It turned out I had to enable "Assert DTR and RTS while COM port open" to make it work. Have you read this page yet?

I took a look over it, but didn't notice this specific observation!

I'll verifiy this.

Thank you.

posted by Jean Rodrigues 22 Oct 2013
Dave Bracey
10 years, 6 months ago.

Wow! I complement your ambition, but you may have jumped in the deep end here.

Do you have any experience designing digital boards? You will need to know what pull-up and pull-down resistors do, and what filter capacitors do, and power regulation, etc.

I'm not trying to be critical, but it kinda sounds like you're just winging it. I would download the design drawings for the MBED LPC1728 platform, and see if you understand all the "stuff" they are putting on that board in addition to the MCU.

Again, disregard this if you know what you're doing :)

No problem, I think I know what I'm doing :) I have an electronics background... but my experience with ARM is limited.

posted by Jean Rodrigues 22 Oct 2013
Jean Rodrigues
poster
10 years, 6 months ago.

Hi,

Just to let you know: I've got it working. I thought it was the missing crystal, but it wasn't. 4Mhz is enough to make ISP working.

In fact, everything was connected perfectly, but the decoupling capacitor was really need (I've just inserted an electrolytic one - 10uF between Vcc and GND) and voi lá.

Thank you for your support.