SparkFun Forums

[dimitrin]

anybody out there connect and get a pic to communicate with the gm862 ev1b?

I have been connecting just the tx and the rx and ground and communicate but the gm862 is not receiving it as a command.

anybody doing this?

is there a hex inverted needed or maybe a max232 needed?

I connect the pic to the serial pins and listen through the usb port in hyperterm.

any help would be great.

[jasonharper]

You have to disconnect the EVK's USB chip TX from the GM862 if you want to drive that signal from your PIC. On the EVK1b, remove the solder blob jumper closest to the USB jack.

The GM862's serial lines operate at 2.8V logic levels. If your PIC was also running at 2.8V, you would be able to simply connect RX, TX, and ground. If it's running at a higher voltage, then you need level translators on all signal lines. There are example circuits given in the GM862 data sheets, they are perhaps a bit more complicated than really needed, but they will definitely work.

[dimitrin]

so I snip the jumper just above the usb port and below the gm862.

Then on the serial comm pins to the side of the board, I place a max232 between the pic and the boards tx and rx?

Sorry I am quite ignorant about these things...

thanks for any help

[jasonharper]

A MAX232 converts between 5V logic levels and +/-10V RS-232 levels. It's about the least useful thing you could use here...

There are level translator circuits in the GM862 documentation (I don't recall if they were in the HW guide or the product guide), using transistors and resistors. Or run the PIC at 2.8V, but this may require changing to a LF part, and may just move the problem elsewhere if the PIC needs to interface with any 5V parts.

[dimitrin]

the max232 would be to bring it up from low voltage...

in the harware datasheet there is something called bcr22pn

which is the translator I assume...

and you say there is a way to make one with resistors and such...

or just use a PIC with low power

thanks for all this clearification!