I have connected a ULN2003 to the P1 port of the 89C51.
The ULN2003 drives a 12V DC relay.
Normally the relay fires OK. But every-now-and-then when the relay switches OFF the CPU resets.

The relay has a reverse diode a/c its coil.
The reset R/C combination is bypassed with a 0.1uF cap.
The ULN2003 is also bypassed with 0.1uF cap.
The gnd of the 12V & the 5V are connected at a single point (no gnd loops) at the power supply filter caps.
The track connecting the two gnds has a small inductor in series.

Has anyone come across this type of problem ??
I'd be most thankful if someone can shed some light on this
Thanks a lot

Zoojar L.