LPC812 LPCXpresso Board

Overview

The LPC812 is an ARM Cortex M0 (16K flash, 4K RAM, 30 Mhz) by NXP. A dedicated mbed enabled board is now available. The NXP LPC-800 MAX development board is compatible with LPCXpresso, mbed and Arduino. Target cost is $20 USD. More information is here, here and here. The mbed online compiler is now supporting the device and it is included as one of the mbed platforms.

NXP and Embedded Artists have also released an LPC812 evaluation board (LPCXpresso LPC812). NXP were kind enough to give me an LPCXpresso LP812 for free at a trade show (thanks again!). The mbed online compiler may also be used with this board after some minor modifications and proper wiring. The picture below shows my test setup.

/media/uploads/wim/img_2890.jpg

The board shows the 20pin JTAG/SWD connector (top left), the 6 pin USB-Serial and 5V power connector (left) and two I2C connectors, one of which has a Sparkfun 3V3 to 5V level converter.

Compatibility

The schematics for the LPC800 MAX board are now available and comparison with the LPCXpresso is possible. It is clear that the LPCXpresso does not have the mbed interface. All programming must done using ISP (serial) or through SWD. The LPC800 MAX supports a serial port to the host PC using the mbed interface. The mbed interface uses P0_1 (RX) and P0_6 (TX) for the PC host serial port to the LPC800 MAX. These pins are different from the default serial port as used by the LPCXpresso. That board uses default serial portpins RX (P0_0), TX (P0_4) and it needs a separate USB to serial converter. The same serial port and USB to serial converter are also used for ISP. Note that there is a design issue with the serial RX on the LPCXpresso: the pin is also connected to the trimming pot. This could interfere with the RX line when the pot is at the extreme ends of its range. I therefore used series resistors (330ohm) for TX and RX to the FTDI cable. That works fine. You cant see them in the pic above: they are hidden underneath the LPC812 board.

The USB to Serial converter that was used here has 3V3 voltage levels for TXD,RXD, DTR and RTS. It also provides 5V powersupply to the 3V3 voltage regulator on the carrierboard. The carrierboard provides pushbuttons for ISP mode and Reset. However, Flashmagic also supports automated activation of Reset and ISP through DTR and RTS. This feature is used here to avoid having to press the buttons manually. A couple of Schottky diodes are used to pull the ISP mode and Reset pins low using DTR and RTS.

The LPCXpresso board includes a dedicated SWD programming and debugging link. This link is supported by the LPCXpresso compiler (Code Red) and other tools. This proprietary interface has been physically cut from the LPC812 board shown above. It is possible to electrically disconnect the programming interface without actually cutting the board in half. The carrierboard features a standard 20pin JTAG/SWD connector that allows flashing and debugging using programmers like NXP LPC-Link or Segger J-Link. I also used series resistors for the SWD programmer (visible in the pic) to add some protection to the LPC812 portpins.

The LPC800 MAX supports analog conversion using a separate I2C ADC and DAC (PCF8591). You can find library for the PCF8591 here. The LPCXpresso does not have that feature. The LPC MAX also supports 8 additional digital I/O pins through an I2C portexander (PCA9672). The onboard RGB LED on LPC800 uses the same portpins as on the LPCXpresso board: P0_7 Red, P0_17 Green, P0_16 Blue.

The mbed lib default mode is to use the Internal RC oscillator (IRC) of the lpc812. You need patches only when you wish to use the external X-tal. Note that the LPC800 MAX board is wired to use the internal oscillator, you need to change some solder pads (SJ2, SJ3) when you want to activate the crystal. The LPCXpresso board on the other hand has the X-tal wired. Obviously, you loose some portpins (P0_8 and P0_9) when the X-tal is needed. The X-tal has the advantage of higher accuracy. Timers will have some error when the internal oscillator is used.

Note

Note that until around January 2015 the mbed lib did not use the PLL to run the LPC812 at its rated 30MHz clock. Instead it used the IRC to run at a clockspeed of only 12MHz. The fixed lib should be pushed soon to enjoy a factor 2.5 speed increase! You can also select the XTAL by making the appropriate selection in the file ''system_lpc81x.c" which is part of the CMSIS mbed library sourcecode.

The carrierboard shown above provides a 3V3 voltage regulator, some buffering capacitors and an indicator LED. Power may be provided through the USB-Serial converter or by a separate 5V supply. The LPCXpresso board has no onboard voltage regulator. You should supply it with 3V3. In my setup I use an FTDI that provides 5V supply and feed that to a regulator. Note that newer FTDI cables are available that provide 3V3 rather than 5V. Some offer a jumper or switch to select the voltage.

The I2C port is available on P0_10 (SDA) and P0_11(SCL). A Sparkfun 3V3 to 5 level converter allows I2C communication with 5V devices. The I2C port has been tested with a PCF8574 portexpander and a SAA1064 LED driver (see here), both devices seem to work as expected.

Note

Note that until around January 2015 the mbed lib I2C blockread and blockwrite methods were wrong. This leads to aborted communications. The fixed lib for block operations should be pushed soon. The I2C byte write and read operations were used as workaround although there are also issues with i2c.start() and the subsequent byte write of the slaveaddress. Any delay or interrupt between these two calls leads to unpredictable results.

Example Software

#include "mbed.h"

DigitalOut myled1(LED1);
DigitalOut myled2(LED2);

// Host PC Communication channels
//Serial pc(USBTX, USBRX); // tx, rx ===> Note default Pinnames USBTX and USBRX are wrong for LPCXpresso LPC812 !
Serial pc(P0_4, P0_0); // tx, rx

int main() {
    pc.printf("Hello World from LPC812\r\n");
    while(1) {
        myled1 = 0;
        wait(0.1);      
        myled1 = 1;
        wait(0.9);
        
        myled2 = 0;       
        wait(0.1);
        myled2 = 1;               
        wait(0.9);
        
        pc.printf("*");        
    }
}

Flashing Software

Compile the example software using the online mbed compiler after selecting LPC812 as target. This will result in a binary file (eg hello_lpc812.bin). Convert the binary file into a hex file using bin2hex utility. Note that a recent version of bin2hex is needed to avoid issues with bugs related to code size: bin2hex /4 hello_l8.bin hello_l8.hex Connect a USB to Serial converter (eg FTDI devices). Note my prototype used a converter based on PL2303. Install and run a recent version of (free) Flashmagic to program the device. Note that Flashmagic v7.50 and higher support the LPC800 family. Press ISP and Reset buttons (or wire DTR and RTS) to bring the LPC812 in ISP mode. Flash the code and it will start executing.

/media/uploads/wim/flash_1.jpg

You may use the integrated Flashmagic terminal to observe serial output (default 9600 baud).

/media/uploads/wim/flash_2.jpg

The alternative method for flashing the LPC812 is to use the SWD port. This requires a separate external programmer (eg NXPs LPC Link or J-Link).

First Results

The Hello World software runs. However, that small program takes up 11K, which is >60% of code space (auwch...). This is probably due to the relatively large mbed lib. User code size will hopefully grow at a modest rate. Some quick tests show that the Serial class and the printf() method are very expensive in codesize. Here are some figures for a small testprogram that uses Ticker and I2C objects:

Serial objectCode Size
none3.4k (21%)
declared only8.3k (52%)
putc() used8.4k (52%)
printf() used11.8k (74%)

This issue is known from other compilers also. In many cases a special small footprint version of printf has been developed to address this problem.

Note that the Pinnames.h file refers to the wrong USBTX and USBRX for the LPCXpresso board.

    // Serial to USB pins
    USBTX = P0_6,
    USBRX = P0_1,

The LPCXpresso needs

    // Serial to USB pins
    USBTX = P0_4,
    USBRX = P0_0,

The LPC812 supports several powerful features like a matrix switch for all pins and a capable statemachine controller. Still need to figure out how well that plays with mbed..

Warning

The LPC812 revision 4C has the ISP entry pin on PI00_12 (P0_12). A Low level on that pin during a hard reset or power-on reset will cause the device to enter the ISP bootmode where it expects to be flashed using the serial port rather than start normally. This issue will occur whenever you use P0_12 as DigitalIn (or even DigitalOut) pin that could be at a Low level during a reset. On the LPC800-MAX board this pin is also used as SPI SCK in ''SPI Slave'' mode and this use-case resulted in the problem described here.

References

  • LPCXpresso LPC812 Board link
  • Flashmagic link
  • LPC800-MAX Board link


Report

20 comments on LPC812 LPCXpresso Board:

16 Sep 2013

What did you do to get MBED to compile for LPC812 ?
I cannot get the compiler to work for my shiny new LPC-800-MAX board :(

Cheers

Ceri

16 Sep 2013

Hi Ceri, did you add the lpc device to your set of devices. Click on device select button (top right) in compiler window, then if needed first add and then select the lpc max. The first time you compile the source you may want to select 'compile all' from the compile drop down list. Thats it. Should compile now. Use P0_xx. Note that LED on max will light when pin is set to 0.

18 Sep 2013

Just a bit of code to show Port Expanded ADC working:

#include "mbed.h"
 
DigitalOut myled1(LED1);
DigitalOut myled2(LED2);
 
// Host PC Communication channels
//Serial pc(USBTX, USBRX); // tx, rx ===> Note default Pinnames USBTX and USBRX are wrong for LPCXpresso LPC812 !
Serial pc(P0_4, P0_0); // tx, rx

I2C i2c(P0_10, P0_11);
 
int main() {
    pc.printf("Hello World from LPC812\r\n");
    
       char data[1],vdata[2];
       float a,b;
       data[0]=0x02;        //selecting AIN2 for PCF 8591 //
       i2c.start();
       
       i2c.write(0x90 | 0x0e,data,1);
       
       
           
    while(1) {
        myled1 = 0;
        wait(0.1);      
        myled1 = 1;
        wait(0.1); 
        
        myled1 = 0;
        wait(0.1);      
        myled1 = 1;
        wait(0.1);         

        myled2 = 0;       
        wait(0.1);
        myled2 = 1;               
        wait(0.1);  
                
        myled2 = 0;       
        wait(0.1);
        myled2 = 1;               
        wait(0.5);
        
    {
            i2c.read(0x9e,vdata,1);
            wait(0.3);
            b=vdata[0];
            a=(b/256) * 3.3;
            pc.printf(" the voltage is %f ",a);
    }        
        
        pc.printf("\r\n");        
    }
}

updated from: https://mbed.org/forum/mbed/topic/4269/

Enjoy

Ceri

19 Sep 2013

Hi Ceri, I am developing a class for the PCF8591 at the moment. It is working fine on the LPC1768 but shows intermittent errors on the LPC812. It looks like a problem with the LPC812 I2C libs, but need to investigate further. I will publish as soon as the problem is sorted. Im running tests on the LPC812 LPCXpresso while awaiting delivery of an LPC800 MAX board.

EDIT: problem with the PCF8591 has been fixed. See here for the lib.

19 Sep 2013

Sounds good,

I wonder if there is a 10 or 12 bit version ??

Ceri

19 Sep 2013

The pcf8591 design is at least 25 years old! Newer devices offer more channels and higher resolution. Examples are ad7995 (4x 10 bit), ad7992 (2x 12 bit). Dont know any that include ADC and DAC. However, you can use separate converters on the same i2c bus.

20 Nov 2013

Hi Wim,

I just got my LPCXpresso LPC812 [rev B] working with ISP (using the excellent free (GPL) software lpc21isp v1.93).

It did not work at first, due to a design-fault: the ISP RX node [P0_0] is also connected on the Xpresso to the "Trimming Pot". If the Pot is at one end, or the other, the ISP_RX is crushed with a 220 ohm resistor!

With my FTDI cable, the Pot has to be set to about mid-way to allow the ISP to function OK.

Also, with the ISP connector J7, the Cable you use must be checked: the supply-out from the cable must be 3.3V - or else remove pin 3 (and power the board from external power supply).

21 Nov 2013

Rod Coleman wrote:

It did not work at first, due to a design-fault: the ISP RX node [P0_0] is also connected on the Xpresso to the "Trimming Pot". If the Pot is at one end, or the other, the ISP_RX is crushed with a 220 ohm resistor!

With my FTDI cable, the Pot has to be set to about mid-way to allow the ISP to function OK.

Also, with the ISP connector J7, the Cable you use must be checked: the supply-out from the cable must be 3.3V - or else remove pin 3 (and power the board from external power supply).

I also noticed the issue with the Trimming pot and used series resistors (330ohm) for TX and RX to the FTDI cable. That works fine. You cant see them in the pic above: they are hidden underneath the LPC812 board. I also use series resistors for the SWD programmer (visible in the pic) to add some protection to the LPC812 portpins.

The LPCXpresso board has no onboard voltage regulator. You should supply 3V3. In my setup I use an FTDI that provides 5V supply and feed that to a regulator. Note that newer FTDI cables are available that provide 3V3 rather than 5V. Some offer a jumper or switch to select the voltage.

23 Nov 2013

Hi Wim, have you seen a schematic for the rev B LPCXpresso LPC812 ?

The rev B is changed to follow the change of ISP-enable pin (from P0_1 to P0_12 on LPC812 TSOP/SOP chips marked 4C & later). Sadly, the rev B does not fix the flaw with the trimmer pot. I don't know if there are more hazards like this.

23 Nov 2013

Rod Coleman wrote:

Hi Wim, have you seen a schematic for the rev B LPCXpresso LPC812 ?

The rev B is changed to follow the change of ISP-enable pin (from P0_1 to P0_12 on LPC812 TSOP/SOP chips marked 4C & later). Sadly, the rev B does not fix the flaw with the trimmer pot. I don't know if there are more hazards like this.

Yes, I have seen the rev B schematic. Looks like the ISP pin is the only change. However, both my LPCXpresso board and my LPC800 MAX board have the first revision LPC812 devices.

I have been considering to modify the LPCXpresso somewhat to align it more with the LPC800 MAX. The changes would include: removing the X-tal bridges and let the LPCXpresso use the internal oscillator (freeing up pins P0_8 and P0_9 and wiring these to the external headers), add a 3V3 voltage regulator on the LPCXpresso small experimentation area. The board would accept 5V input on Vin pin2 and provide 3V3 out on pin 28 (which is the same as mbed pin40).

31 Dec 2013

Can I use the LPC link to program other LPC mcu if ever I want to make my stand alone board?

31 Dec 2013

Hi Felan, the LPC link part of the LPCXpresso board is really just a SWD programmer. It can be used with other LPC processors on your own boards. However, the LPC link uses a special driver on the PC side that only works with the LPCXpresso toolset as far as I know. You would probably be better of with a generic JTAG/SWD programmer like Segger J-Link or use one of the mbed programmers like the one on the LPC812 MAX board (find the example page on mbed). Note that you can still use the mbed online compiler to flash any of the supported LPC devices using a tool like J-Link.

31 Dec 2013

I use the LPC Link, mostly because I have it around and I already use the LPCxpresso IDE, without any issues. There is a toolbar button that is used to flash a chip with an already compiled binary file like one you get from the MBED online compiler.

Just make sure you design the board so you have access to the SWD pins.

You can also look into UART0 ISP bootloading which uses less hardware and pins. The downside is there is no debugging capability even with the LPCxpresso IDE.

31 Dec 2013

Wim Huiskamp wrote:

Hi Felan, the LPC link part of the LPCXpresso board is really just a SWD programmer. It can be used with other LPC processors on your own boards. However, the LPC link uses a special driver on the PC side that only works with the LPCXpresso toolset as far as I know. You would probably be better of with a generic JTAG/SWD programmer like Segger J-Link or use one of the mbed programmers like the one on the LPC812 MAX board (find the example page on mbed). Note that you can still use the mbed online compiler to flash any of the supported LPC devices using a tool like J-Link.

The mbed programmer was spot on! It was what I really wanted to ask and do in the first place :D I think i'm going to have to invest on a Segger J-link as I'm also experimenting with Freescale's kinetis mcu. Thank you for your response! :D

07 Jan 2014

Hai

I am working on lpc-812.I have build the code no errors and i have started debug there i got the error.The error is

Failed on connect: Ep(01). Target marked as not debuggable. Conn&Reset. Was: None. DpID: BC11477. Info: HID64HS12 can any one help on this error.

07 Jan 2014

From my experience this is a general error when the micro has trouble or is completely unable to communicate using LPC Link (probably any debugger).

I have seen this when - The SWD wires were not hooked up correctly - The LPC812 was not powered. The debugger might not supply power depending on the board or design. - The SWD pins are not setup correctly. I try to use the default SWD pins just in case. - Other circuits caused the micro not to function correctly.

Are you using this on your own LPC board design, LPCXpresso or the LPC800-Max? It would help if we knew what board you are using.

Hope this helps.

11 Jan 2014

I am using LPC-812 in LPCXpresso.I am not able to understand what is the problem Exactly.

11 Jan 2014

vijay bhaskar wrote:

I am using LPC-812 in LPCXpresso.I am not able to understand what is the problem Exactly.

vijay bhaskar wrote:

I am using LPC-812 in LPCXpresso.I am not able to understand what is the problem Exactly.

11 Jan 2014

I am using LPC-812 in LPCXpresso along with the IDE. I too see the same error which Vijay reports. I connected the UART TX and RX pins of the LPC-812 to the host PC running the IDE. When the IDE was reflashing my code, I temporarily grounded the ISP pin on the LPC-812. Then, the error was gone and code runs properly.

But, some time later during next flashing of the code, I see this error again. Is there some way this could be controlled from the IDE?

Thanks in anticipation, Niranjan

11 Jan 2014

Niranjan Udipi wrote:

I am using LPC-812 in LPCXpresso along with the IDE. I too see the same error which Vijay reports. I connected the UART TX and RX pins of the LPC-812 to the host PC running the IDE. When the IDE was reflashing my code, I temporarily grounded the ISP pin on the LPC-812. Then, the error was gone and code runs properly.

But, some time later during next flashing of the code, I see this error again. Is there some way this could be controlled from the IDE?

Thanks in anticipation, Niranjan

The lpc812 is programmed and debugged using its SWD port. The SWD portpins may also be used as regular portpins when you remap them through the switchmatrix. That may lead to disabling of the program and debug functions. Only a hard reset to ISP mode at poweron can re-enable the SWD functionality. Are you using the SWD pins for anything else? Are you using the switchmatrix at all? I have seen forum reports that there were bugs in some lpcxpresso code examples that used the switchmatrix and unintentionally disabled the SWD pins. Checkout the lpcxpresso forum for lpc800 and/or lpc812 .

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