Sharing same LCD between two microcontroller boards.

[savvej]

thanks for pointing out .I need to put pull down resistors from resistor to ground..

 

[ericgibbs]

thanks for pointing out .I need to put pull down resistors from resistor to ground..

What value of pull down resistor do have in mind.??

 

[savvej]

So now the diode design should work right??

 

[savvej]

10k ..but any higher value will be ok..right??

 

[savvej]

resistance value should be much greater than input impedance of LCD pin,right?

 

[ericgibbs]

resistance value should be much greater than input impedance of LCD pin,right?

Hi,
The input resistance of the LCD logic is VERY high.
Its important that you consider the response time of the diode/resistor combination in order to keep the low going 'edges' of the signals going to the LCD within the required specification.

As the LCD pin low going signal is not an active pull down [ ie: direct connection to a PIC pin], it important that the passive pull down resistor is low enough to get a fast edge.
I would consider a pull down resistor of 4K7.

 

[savvej]

Adding diodes and 4k7 resistor did'nt work.

But why so?(Currently have solved problem by adding some dpdt switch to connect LCD to required board while operating.)

 

[ericgibbs]

Adding diodes and 4k7 resistor did'nt work.

But why so?(Currently have solved problem by adding some dpdt switch to connect LCD to required board while operating.)

Where did you add the resistors to the circuit,, post a quick sketch