Many new notebooks do not have a serial port any more: everything is USB. This can lead to problems (see USB or not: CDC with Processor Expert) as many embedded targets  use normal RS-232. In my classes I’m using the Tower boards: some Tower boards have an on-board 2 pin RS-232 header, e.g. the Tower TWR-MCF52259. Others like the TWR-K60N512 use the added TWR-SER board. The Tower boards have as well a USB capable S08JM60 which is used for debugging (OSBDM/OSJTAG), so why not using the OSBDM microcontroller as Serial-to-USB gateway?

The good news is: P&E just has released a new version of the Open Source OSBDM/OSJTAG firmware which enumerates as a USB CDC device on the host PC: that way the target microcontroller can use the OSBDM/OSJTAG device on the board to communicate with the host. OSJTAG/OSBDM acts as a Serial-to-USB converter :-).

The steps below explain how to install and use the feature with CodeWarrior for MCU10.2.

Downloading new Firmware

First, I need updated OSBDM/OSJTAG firmware. It is available from http://www.pemicro.com/osbdm. On that site I select ‘Firmware Updates & Recovery’:

This will ask me to sign into my P&E user account. You can request your own user account with ‘Create New Account’ link:

The next step is to download the firmware_updater_install.exe (around 8.2 MB):

The next step is to install the software. If there is an earlier version of the firmware updater, it needs to be uninstalled first: the installer will take care about this.

Flashing new Firmware

After everything is installed: let’s run the P&E Firmware Updater Utility from the shortcut created:

I have my board connected to my laptop, and I use in the screenshots the TWR-MCF52259. Under point 1) I select OSBDM/OSJTAG:

Under point 2) it lists my connected board with the firmware version (30 in this case). The firmware version which has USB CDC support is version 31 (point 4). So I’m going to update my existing firmware version 30.21 to the new version 31.

I press the ‘Update Firmware‘ button. This will prompt a dialog to set the OSBDM/OSJTAG bootloader jumper:

The bootloader jumper is labeled BTLD on my board:

Tip: In case no jumper is at hand, there is a trick. The bootloader jumper is only checked at power-up of OSBDM. No need to shortcut it all the time. I help myself with a paperclip to shortcut the jumper right at power-on-reset 🙂

I disconnect the board, set the jumper and power again the board.

Note: All LEDs on the board will be off!

Windows will install the drivers for the bootloader (if not already installed). Then after pressing OK, the bootloader will flash the new firmware:

After that, a dialog asks to enter run mode again:

So unpower again, removing the bootloader jumper, power the board again.

If everything was going fine, this is indicated in the dialog:

Connecting the board to the host will start a new USB enumeration, and drivers get installed:

Now the board should enumerate as CDC Serial Port in the Windows Device Manager:

Ready to use that board with that CDC Serial Port…

USB CDC with OSBDM on TWR-MCF52259

First I need to find out how the RX an TX lines of the OSBDM/OSJTAG are connected to my microcontroller. For the TWR-MCF52259 this looks like this:

Following the signals: I need to set the jumpers J12 and J13 to the 2-3 position to connect the MCU_TXD0 and MCU_TXD0 lines to the S08JM60 which runs the OSBDM:

Example Project

First, I want to verify that things are working with the normal RS-232 UART. I create a test project which writes to the console. The simplest thing is to create a Processor Expert project and using the Term component:

The TWR-MCF52259 board is using the UART0 for the on-board serial connector, and I configure it for 38400 baud:

The test program is simple: writing a string to the terminal in an endless loop:

static void TestSerial(void) {
  int cnt = 0;

  for(;;) {
    Term1_SendNum(cnt);
    Term1_SendStr(" Hello World!\r\n");
    cnt++;
  }
}

First, I try this with the UART0 signals routed to the physical COM port on the board, having J12 and J13 set to the (default) 1-2 position:

The menu Window > Show View > Terminal opens a terminal program which I configure to use COM1. And voilà: my test program writes to the physical COM1 port :-):

Now the same application shall work with the serial lines routed to OSBDM. Now I change the jumpers J12 and J13 to the 2-3 position:

Now connecting to the virtual COM port 37, and it works through OSBDM and USB too :-):

Note: it seems that some terminal applications have problems to keep up with the traffic coming from a virtual COM port. I’m able to crash e.g. Termite, but it works fine with the the built-in Eclipse Terminal view. So if you see issues with the P&E OSBDM/OSJTAG USB CDC implementation, it is likely that there is a problem in the terminal program, not in OSBDM/OSJTAG.

USB CDC TWR-MCF51CN128

Now trying the TWR-MCF51CN128. This one was one of the first Tower boards available, and very similar to the TWR-52259 one: it has as well two jumpers to direct the UART traffic either to the on-board 10pin header or the OSBDM S08JM60. However, I was not able to get the UART  traffic routed through OSBDM. I’m not sure, but this could be a problem of the board and the circuit on it? At least it is not working for me :-(.

USB CDC with OSJTAG on TWR-K60N512

Next board to try is the TWR-K60N512. This board had no on-board serial connector. So if I want to use a terminal with this board (without the TWR-SER), I really need USB CDC over OSJTAG. As for the TWR-MCF52259 board, I need to upgrade the firmware on the board. The schematics for the board is different: no jumpers for the serial bridge:

The schematics tell me that TX and RX lines are connected to PTE8 and PTE9 of UART5 on the K60 microcontroller:

This time I’m going to change my SD Card application for K60 to use the serial bridge. For this I disable the existing AS1 Serial_LDD (which was using the serial port on the TWR-SER) and add a AS1 to connect to the serial bridge:

The new Serial_LDD is configured to use the UART5:

And within minutes, I have the application running on the board, using the virtual bridge on COM37 :-):

The cool thing is that now I do not need the TWR-SER any more: I can run my application with shell support run on a single board, with a single USB connection for power, debug and console:

🙂

Summary

What P&E has added to OSJTAG/OSBDM in their latest firmware is a big step and improvement for me: Now I can use a single connection for power, debug and terminal connectivity. If I have OSBDM/OSJTAG on my board, then I can avoid to run a native USB CDC stack. That makes my life much simpler and easier. And with the exception of the TWR-MCF51CN128, it works perfectly for the TWR-K60N512 and TWR-52259.

Happy Virtualizing 🙂