Interfacing a uM-FPU using AXE027

[VK4CP]

Here is a simple adapter I have been using to connect the uM-FPU IDE via AXE027 USB PICAXE cable.
Basically, an inverter in both directions, with appropriate pullups and pulldowns.
It is easy to add this to a breadboard prototype.

Although the uM-FPU's SERIN port in 5V tolerant, it is [correctly] pulled up to the uM-FPU's +3.3V rail.

You could also use a hex inverter IC, such as;

Not forgetting to wire up VCC, VSS, and it's good practice to tie all unused inputs high or low.



Cam, from MicroMega also writes;

Another thing to note, is that the FPU checks SERIN at reset to determine if the debug monitor should be enabled.
IF SERIN is low, the debug monitor is disabled.
So make sure the AXE027 is connected through the inverters to the FPU, before reset.

Once connected, you should see a reset message whenever a reset occurs.
Try the Debug>Read Version to display the FPU version string.
If you add a TRACEON instruction at the beginning of your code, and you can see a trace of all the instructions as they execute.
You can use a BREAK instruction to stop execution, then single step through your code with the Step button.
Registers contents are displayed on the right.
Right click on the register value to select the desired format (e.g. hex. long, float).
See IDE documentation for more details.

 

[MPep]

Thanks for posting this. I too have been thinking of using the uM-FPU64 for a project and info such as this is very valuable.

 

[westaust55]

As a variant which makes use of a hex inverter chip and the switching mechanism of the standard stereo programming socket to prevent entering Debug mode when the programming cable is not inserted, have a look at the schematic attached to post 2 here:
http://www.picaxeforum.co.uk/showthread.php?15195