Looking for an NXP ARM CM0 reference design

[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