()blivion
Active Member
Hello all, getting directly to the point...
A while back, I was developing a project that used a PIC and a LCDM together, and for no apparent reason the two devices destroyed each other. After investigating the situation, I could only conclude that my PIC asm code must have made a port pin zig when it should have zaged. In other words, one line was logic high on one end of the wire, and logic low on the other. With both push-pull drivers having low-Z and thus nothing to stop massive current from flowing, mutual destruction of the die for each IC in sued.
This unfortunate incident got me thinking about how I had the PIC attached to the LCDM directly and how to go about changing the interface to make it intrinsically safe should such code failure ever happen again. Here is a picture of the I/O circuit for the chip out of the STU066U datasheet. . . I assume the PIC I/O is similar.
View attachment 68884
I was thinking about just a 500~1000 Ohm resistor in series with all the lines to limit current to the max each driver should be able to handle. But I'm worried about slew rate and impedance matching and such things, though I honestly don't know if that will apply to something like this. It can only run at >500Khz I believe, but don't quote me. It's in the datasheet I'm sure.
Any incite and useful advice would be appreciated. Thanks for your time.
-()b
A while back, I was developing a project that used a PIC and a LCDM together, and for no apparent reason the two devices destroyed each other. After investigating the situation, I could only conclude that my PIC asm code must have made a port pin zig when it should have zaged. In other words, one line was logic high on one end of the wire, and logic low on the other. With both push-pull drivers having low-Z and thus nothing to stop massive current from flowing, mutual destruction of the die for each IC in sued.
This unfortunate incident got me thinking about how I had the PIC attached to the LCDM directly and how to go about changing the interface to make it intrinsically safe should such code failure ever happen again. Here is a picture of the I/O circuit for the chip out of the STU066U datasheet. . . I assume the PIC I/O is similar.
View attachment 68884
I was thinking about just a 500~1000 Ohm resistor in series with all the lines to limit current to the max each driver should be able to handle. But I'm worried about slew rate and impedance matching and such things, though I honestly don't know if that will apply to something like this. It can only run at >500Khz I believe, but don't quote me. It's in the datasheet I'm sure.
Any incite and useful advice would be appreciated. Thanks for your time.
-()b
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