ICSP with using an LCD tied to RB6 & RB7

[enauman]

Iam using an older demo board from Microchip. The MXDEV Analog evaluation driver board and the Digital Pot evaluation board. The problem I am having is getting the ICSP to work with the LCD plugged in. The RB6 & RB7 lines are shared with LCD data lines. The melabs usb programmer won't do it's job unless I unplug the LCD. I downloaded the data sheet for the LCD but it doesn't have any electrical specs on the data lines except logic levels required. No mention of input impedance. My question is do any of you have experience with this particular board regarding ICSP functionality. I was considering cutting the data lines and inserting a switch so I could switch out the LCD when programming through the ICSP connection but I would rather keep the board stock if possible. Any ideas?

[Darrel Taylor]

The LCD shouldn't interfere with ICSP as long as the LCD's R/W pin is held low.

That dev board connects R/W directly to a PIC pin which is tri-stated (floating) during programming. That can cause the LCD data bus to be in read mode, which will interfere with ICSP.

Try adding a pull-down resistor on RB2.

[enauman]

Thanks. That did the trick. I thought about the R/W mode but I forgot that the I/O pins are floating during programming... Thanks again.

Ed