Strange radio comunication problem.

[fuzzy]

HI,

I found out a curious problem yesterday and i still can't undertand it.
I programmed a transmitter and it's radioreceiver using pic16f88. I transmit data from RS232 Pin and i read bata in RS232PIn of another PIC.
I usually connect hem by radio modules. When I wrote firmware everithing worked OK. I produced 50 devices working perfectly.
Now i'm producing other 50 devices but i've got a big problem. I downloaded firmaware on them and they don't work as good as other
some(few) work good but others work very very bad. i would like to understand if it can be a PIC problem or a transmitter/receiver problem.
for example with previous production transmitter , new receiver don't work
while they can work with new production transmitter. and old production receiver works good with both production transmitter. I tryed calibrating internal 8mhz pic's clock and one of them worked better with calibration =-2.
topmorrow i'l try tranferring pic from a old production board to a new production one with same firmaware and maybe i'll understand better.

Anyone has a similar experience?

[PCM programmer]

Call the radio manufacturer and ask them for a detailed list of changes
between the new version and the old version. This would include
signal timing, logic levels on i/o pins, performance over temperature
range, initialization sequences, commands, etc. -- All changes.

[RossJ]

It sounds like your first problem is to determine whether the problem is a radio one (module to module) or a serial one (module to/from PIC).

The way I usually go about detecting serial problems is to monitor the communication (passively) with a PC. An invaluable tool is a simple cable which connects the receive and transmit lines back to a PC's receive line on two COM ports. This allows you to monitor the data flow in both directions between the PIC and radio module. I use a program called Docklight (http://www.docklight.de/) on the PC to view the data. Note, if the voltage levels you are monitoring are TTL (i.e. a direct connection between PIC and module), you will need to add a MAX232 or similar level converter into the monitor cable.

If you do much with RS232 type serial comms, this is an invaluable tool.

A quick check you can make is to count the number of framing errors detected by the PIC. With a short direct wired connection, the number of errors should be extremely low.

Another thing to consider is voltage levels. The radio module I use is powered from 5 volts, but internally runs at 3.3 volts. The inputs are 5 volt tolerant, but the outputs are only 3.3 volts. On the 18 series PIC I am using, the USART pins have schmitt trigger inputs. The voltage thresholds are incompatible with 3.3 volt signals. Having said that, it usually works. But perhaps not always.

/Ross.

[fuzzy]

I made some experiments. I found out it's a pic problem.
I swapped pic between an old device and a new one and the not working new one begun working nice while the old one didn't work as well.
then i used a pic 16f87 i had for other purpose and device bean working perfectly.
I can see that the new 16f8 pic don't work in receiver but work in transimitter very well, i think i'm going to change all of them. I also found out that device works good witha pic16F88/ESS intead of 16F88/ISS

why does it happen in your opinion??

[Humberto]

Are you aware of a Microchip silicon errata that will affect the internal RC oscillator in
16F87/88 under special conditions?
Read this, may be you can apply a work around.

http://ww1.microchip.com/downloads/en/DeviceDoc/80171k.pdf


Humberto