Data eeprom issue

codewrecker2 · Joined: 23 Dec 2005 Posts: 23

guyz,i have been using pic16f689 for a while for a monitoring system,without any problems.but sometimes when i read the data eeprom and put it in a packet for rs232 transmission,it reads the higher byte as FF and lower byte FC(am storing a 16bit number in eeprom,max being 3000) and the other part of the data packet remains intact.i have tried changing the pic,but same problem.
Note:i have taken care while programming to separate the read/write cycles for the pic,so i dont think its because of some read/write clash.does anyone have a clue wotz wrng?

King Virus · Joined: 02 Mar 2006 Posts: 14 Location: Italy

rberek · Joined: 10 Jan 2005 Posts: 207 Location: Ottawa, Canada

I also had this happen recently.

I was building the 16-bit Tx data by shifting the "upper" memory byte left by 8 positions and ORing it with the "lower" memory byte. I had declared the upper byte as an int16, because of the shift, but left the lower byte as an int8 since I wasn't shifting it. This turned out to be a problem, so I declared the lower byte as an int16 and masked it with 0x00ff. Then the unwanted FF's went away.

Dumb mistake on my part, but is was very intermittent in the actual circuit, so I assumed it was noise or something.
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