Looking for an NXP ARM CM0 reference design

[apelly]

I have 3 or 4 projects in the planning phase, some more advanced than others, that require a smallish MCU.

While I was browsing element 14 the other day I found some NXP LPC11U35FBD48s on sale for 3 NZD each. They seem to tick a lot of boxes:

• LQFP48
• 64k Flash
• 10k RAM
• 4k EEPROM
• 3.3v
• 5v tolerant digital I/O
• Built in USB

I bought 10. I figure I'll break a couple, a couple will end up on non-functional boards, and they're overkill for some things I want, but it'll be helpful to focus on one chip for a while.

Here's the NXP marketing wank overview, the datasheet (pdf), and the user guide (pdf)

Anyway; for the life of me I can't find a reference design. I've been following dannyf's cool thread STM32, ghetto style, and he's doing nothing! Presumably more effort is required for something reliable? Maybe the things are so robust it doesn't matter. There are a few notes in the datasheet, but it seems far from comprehensive.

I'm particularly interested in the reference voltage and decoupling. Any thoughts?

[Marco]

Couldn't you get that from the schematics for one of the LPC11U37 boards? (Same micro with more Flash AFAICS.)

[apelly]

You'd bloody think so wouldn't you? Granted, I was tired when I was looking yesterday, but I couldn't see schematics posted anywhere.

If you've seen them anywhere could you give me a clue where you were looking please?

[Jeroen3]

Well then. Let me google that for you. (Notice the LPC11Uxx, where the xx only specify minor diffcerences in perihperal count, speeds or memory sizes due to yield rates or marketing e.g....)
http://www.keil.com/support/man/docs/mcb1000/mcb1000_to_schematics.htm
http://www.embeddedartists.com/products/lpcxpresso/lpc11U14_xpr.php
http://www.nxp.com/demoboard/OM13032.html

Or maybe a design based on a LPC11U24, http://bit.ly/Z4biXQ. (Quality not guaranteed, rush project)

And the "official" nxp support site. No, that isn't nxp.com
http://www.lpcware.com/content/device/lpc11uxx

[apelly]

http://www.keil.com/support/man/docs/mcb1000/mcb1000_to_schematics.htm
http://www.embeddedartists.com/products/lpcxpresso/lpc11U14_xpr.php
http://www.nxp.com/demoboard/OM13032.html

Or maybe a design based on a LPC11U24, http://bit.ly/Z4biXQ. (Quality not guaranteed, rush project)

And the "official" nxp support site. No, that isn't nxp.com
http://www.lpcware.com/content/device/lpc11uxx

Really? You found those in only a couple of minutes? I've literally spent hours and come up empty.

Well then. Let me google that for you. (Notice the LPC11Uxx, where the xx only specify minor diffcerences in perihperal count, speeds or memory sizes due to yield rates or marketing e.g....)

Now, now; no need to take the piss 

What's the skill I'm missing? Simple abbreviation, by the looks of it.

Anyway, thanks mate! That's awesome.

[Jeroen3]

It a thing you will learn when working with nxp products. You don't find a consolidated collection of useful documents at the obvious places.
But they are improving, slowly.
It also helps a lot if you know their part naming scheme.

[HackedFridgeMagnet]

It a thing you will learn when working with nxp products. You don't find a consolidated collection of useful documents at the obvious places.

NXP and STMicro are more similar than I realised.

[nctnico]

It a thing you will learn when working with nxp products. You don't find a consolidated collection of useful documents at the obvious places.

If you look at the device on their website there is a link to a zip file containing ALL the documents (datasheets, user manual, errata)!

[dannyf]

I can't find a reference design.

First of all, what is a "reference design" isn't entirely clear. What is required for a particular application will depend on that application.

Some "practical" minimum would be connecting all Vdd/Vss; decoupling on Vdd/Vss; and decoupling to VDDA / Vref (if it has one).

After that, you may implement RESET; Crystal; or SWD/JTAG; or external Vref; Some chips have Vcap and you will need to connect those as well....

As the STM32 thread shows, those chips are surprisingly robust and a truly minimalist board can work. It may not be advisable for certain applications, however.

[apelly]

If you look at the device on their website there is a link to a zip file containing ALL the documents (datasheets, user manual, errata)!

Yep. Sure is.

None of those docs have schematics though. Not that I found. Compare those docs (most of which are very useful) with the links above from Jeroen3

Edit: Damn my spelling!

[mikeselectricstuff]

Find some devboards, look at their schematics.
On NXP parts, one gotcha is there is typically at least one pin that needs to be pulled to determine whether a bootloader runs at startup.

[tszaboo]

Indeed, there should be more useful information also for the hardware designer at the devices' webpage. Battery powered, and mains powered reference designs. They probably dont realize that this sis the correct place to sell their own power management/reset and other support circuits.
For NXP, I would look for the LPCexpresso boards, buy one, download schematic, that should help.

[Jeroen3]

Find some devboards, look at their schematics.
On NXP parts, one gotcha is there is typically at least one pin that needs to be pulled to determine whether a bootloader runs at startup.

In case you forget this, most of nxp's bootloaders search for a pattern at a predetermined address in flash to disable the bootloader. So, always put the swd on a header.

Few manufacturers include full reference design schematics, some have application notes (appnote) or examples in the manual, such as ftdi.

If you look at the device on their website there is a link to a zip file containing ALL the documents (datasheets, user manual, errata)!

Thats a recent addition, not all parts had that a while ago. But it's a good thing.
LPCware usually has the latest documents.

[nctnico]

The link to the zip file has been there for at least 8 years for about every NXP ARM controller I ever used  O0

[jakeypoo]

I'm using an embedded artists lpc11u35 board. Link:

http://www.embeddedartists.com/products/boards/lpc11u35_qsb.php

Schematic is there but you have to log in. (It's a pretty bare bones board)

[nctnico]

If you look for example schematics for NXP's ARM controllers: Keil has a wide range on their website. Most include some extra circuitry to allow serial port programming using the bootloader & the Flashmagic software.

[sporadic]

Not directly related, but Atmel is pretty good at having "schematic checklists" that tell you what all needs to be connected and how for correct chip operation.  Power, debugging / programming, reset, etc... For their Xmegas, this was a separate appnote.  For the Atmel D20 (CM0+), they include it in the datasheet itself - http://www.atmel.com/Images/Atmel-42129-SAM-D20_Datasheet.pdf (page 607).

[zapta]

Well then. Let me google that for you. (Notice the LPC11Uxx, where the xx only specify minor diffcerences in perihperal count, speeds or memory sizes due to yield rates or marketing e.g....)
http://www.keil.com/support/man/docs/mcb1000/mcb1000_to_schematics.htm
http://www.embeddedartists.com/products/lpcxpresso/lpc11U14_xpr.php
http://www.nxp.com/demoboard/OM13032.html

Or maybe a design based on a LPC11U24, http://bit.ly/Z4biXQ. (Quality not guaranteed, rush project)


And the "official" nxp support site. No, that isn't nxp.com
http://www.lpcware.com/content/device/lpc11uxx

Here is another minimal design from embedded artists

http://www.embeddedartists.com/products/boards/lpc11u35_qsb.php

[Jeroen3]

Cool a small breadboardable ARM with the swd header!
Those people also sell genuine ulinks for an afforable price, great combo.

None of that lpclink crap, down to the bare metal wil keil 

[apelly]

Thanks for the info guys. Like most projects, it'll be months before I have anything to show for this, but I'll be sure to post when I do.

[zapta]

I'm using an embedded artists lpc11u35 board. Link:

http://www.embeddedartists.com/products/boards/lpc11u35_qsb.php

Schematic is there but you have to log in. (It's a pretty bare bones board)

Is there a way to check the schematic before buying it? I logged in but it asks me for a serial number.

[jakeypoo]

Is there a way to check the schematic before buying it? I logged in but it asks me for a serial number.

Surprisingly, it's very hard to find online. Either no one uses the board, or they are good at keeping it from being public (I don't know why they would).

It's very basic.
 - USB line protection & plug in detection.
 - 3V3 LDO
 - Undervoltage reset generator IC
 - SWD header
 - Switches reset & for selecting USB/UART bootloader
 - Some LEDS

If you really want the schematic, PM me and I can send it to you. Don't want to get Dave in trouble by posting it here. 

[dannyf]

Lots of information / schematic about those things in the lpcxpresso user manuals.

[zapta]

Is there a way to check the schematic before buying it? I logged in but it asks me for a serial number.

Surprisingly, it's very hard to find online. Either no one uses the board, or they are good at keeping it from being public (I don't know why they would).

It's very basic.
 - USB line protection & plug in detection.
 - 3V3 LDO
 - Undervoltage reset generator IC
 - SWD header
 - Switches reset & for selecting USB/UART bootloader
 - Some LEDS

If you really want the schematic, PM me and I can send it to you. Don't want to get Dave in trouble by posting it here.

Is the undervoltage reset generator IC really required?

(I plan to use it as a minimal circuit design example for my own custom boards).

[ElektroQuark]

Doesn't the BOR behaves similarly?

[zapta]

This link has detailed schematics, BOM and and code examples for minimalist NXP M0.

http://eewiki.net/display/microcontroller/Getting+Started+with+NXP's+LPC11XX+Cortex-M0+ARM+Microcontrollers

[SirNick]

I just sent this to the fab -- it's my first ARM project, so I can't vouch for it yet.  But, if there are any glaring issues, maybe the guys here can rip it to shreds and we'll both benefit.

[nctnico]

Is the undervoltage reset generator IC really required?

I never use one with the Cortex Mx controllers from NXP. They have their internal power-on-reset circuitry.

[zapta]

Is the undervoltage reset generator IC really required?

I never use one with the Cortex Mx controllers from NXP. They have their internal power-on-reset circuitry.

It's connected to the reset button. Is it possible to have a reset button with the internal power-on-reset?

[zapta]

I am looking at the minimal LPC11U14 circuit in page 4 here (this is the target side of the LPC11U14 LPCExpresso board.

http://www.embeddedartists.com/sites/default/files/docs/schematics/LPCXpressoLPC11U14revA.pdf

What is the purpose of Q3?  The LPC11U35 Quick Start board has a similar arrangement which the manual describes as follows: " There is also a USB connect functionality to connect a 1.5Kohm resistor to the USB-DP signal. "

[Jeroen3]

Q3 is USB soft connect. Which can "reset" the USB connection. To force re-enumeration by the host.
The bootloader uses it to signal it's done using the USB-MSC or USB-DFU class to the connected host.

[zapta]

Q3 is USB soft connect. Which can "reset" the USB connection. To force re-enumeration by the host.
The bootloader uses it to signal it's done using the USB-MSC or USB-DFU class to the connected host.

Thanks Jeroen3. Can I achieve the same effect by manually reconnecting the USB when the bootloader is done?

(trying to minimize the circuit).

[SirNick]

Yes, technically.  It's not primarily a reset signal, per-se.... It's how the USB host knows there's a device on the other end.  By turning on the transistor, you pull the line (either D+ or D- depending on the device speed you're advertising) to 3v3.  It goes through a resistor (pull-up) because the data line still needs to serve as part of the differential pair.

If you need to reset the bus, you can drop the pull-up, signalling a device disconnect, and then pull it high again to re-enumerate.  You could use a resistor to 3v3 alone... however.... your MCU is not likely to be fully booted before the host starts interrogating your device, so you may end up with "device malfunction" errors without a means to delay presence detect until the code is ready to participate on the bus.

[zapta]

Yes, technically.  It's not primarily a reset signal, per-se.... It's how the USB host knows there's a device on the other end.  By turning on the transistor, you pull the line (either D+ or D- depending on the device speed you're advertising) to 3v3.  It goes through a resistor (pull-up) because the data line still needs to serve as part of the differential pair.

Thanks for the explanation. I will hook a scope and will look at the timing.

How come this functionality, which is part of the USB protocol, not implemented inside the MCU? After all it does have USB controller.

[zapta]

Surprisingly, it's very hard to find online. Either no one uses the board, or they are good at keeping it from being public (I don't know why they would).

It's very basic.
 - USB line protection & plug in detection.
 - 3V3 LDO
 - Undervoltage reset generator IC
 - SWD header
 - Switches reset & for selecting USB/UART bootloader
 - Some LEDS

If you really want the schematic, PM me and I can send it to you. Don't want to get Dave in trouble by posting it here.

Got the board today and like it. It's small and minimal, similar to the Arduino Mini Pro on which I used previously as a reference design. Hooked it to a computer and saw the bootloader USB file system with the binary file (great for firmware update by end users).  Will start programming it today (I already have the LPC Link and got this cable from digikey SAM8218-ND). Life is good.

[Jeroen3]

How come this functionality, which is part of the USB protocol, not implemented inside the MCU? After all it does have USB controller.

Because it takes time to boot up the USB controller.

An small article on this pin:
http://learnembedded.blogspot.nl/2009/11/embedded-artists-lpc-2148-usb.html