LINX RF module and PIC

[Michael]

I have a pair of 16c65B, one as a xmtr using serout and the other as a rcvr using serin.

When I hardwire the output pin to input, everything works great. I normally have an optoisolator in there and it works fine either way...with or without.

I bought a LINX ES 916mhz xmtr and rcvr module and was hoping that it would be a simple plug and play but so far, no luck.

I have a scope connected to the data output on the rcvr module....the data is there and looks fine but when I connect to the rcvr pic (or the opto), I lose the waveform and get nothing.

I tried some series resistance, which gets the waveform back but still no action on my rcvr.

Could someone tell me what I'm doing wrong?

It has to be something simple.

I even inverted the data for the heck of it but obviously this is an interface problem as I'm losing signal completely.

--thanks

[Michael]

I did now just notice one thing that may play a part.

I'm using A4 as my input pin for SERIN on the rcvr and I know it's a schmitt trigger input (didn't know that before I did the pc board).

But like I say....if I hardwire....everything is fine.

I'll try another input and see but I don't think that's it.

?

[Michael]

actually, come to think of it, I made porta.4 serin BECAUSE of the schmitt trigger.

works wired...just not with the linx.

[Bruce]

On most PICs RA4 schmitt trigger inputs require a minimum input level of around 0.8 * Vdd to be recognized as a logic 1. Assuming you're running right at 5V, this would be around 4V.

The Linx ES series receiver data output level for a logic 1 is around Vcc - 1.1 min, Vcc - 1 typical, or Vcc - 0.9 max. You only have around 3.9V min to ~4.1V max. Best case is around .1V above the minimum level required by RA4, so this could be a problem.

A TTL input would have been nice, but you can always use an FET or transistor.

[Michael]

Both my linx rcvr and the pic are powered by 5v supplies (seperate) so I sort of ruled out a threshold problem but I thought of just using a transistor buffer last night to see if that solves it.

I thought the linx out and the pic input would be compaible as most schematics
I've seen show a direct connection.

It's like when I connect the linx, it just shorts out the signal completely.

I'm gonna goof with it later....I'm sure it will be something stupid.

[Michael]

Well....I tried a buffer into the pic (inverted and not)...plenty of data on the SERIN pin and still nothing.

I don't get it....it works perfectly with a wire pair but nothing with the Linx.

How important is a squelch circuit?

I'm not using one.