lcd initialize problem bcoz of hardware.......

Dear friends,




I have an application where i am using:

1.pic18f46k80 controller
2.4 line lcd (jhd 204a).
3. mcp2200 usb to serial uart..

Microcontroller's tx rx are connected to mcp2200's rx and tx resp.and the ground is common for uC and Lcd and mcp2200 ,
But uC and lcd are supplied via a different Vcc 5V(main supply) , and the mcp2200 is usb powered.....


The problem comes when i power off then power on the system , the lcd shows the garbage value.
if i reset the controller it works ok ....

The thing is that the mcp2200 which i m using remains connected to the usb device(laptop) and so there is power in the circuit , the Controller shows 2.8 v around it and so does the lcd wen the main application power Vcc is switched off.
When i switch on the circuit , the lcd is not able to properly initialize coz there was already some volts across it....


Please suggest what could be done in order to completely detach the lcd and uC , from mcp2200 usb power supply wen the device is switched off....

Thanks and regards
Jitender

When u reset the microcontroller, if it works ok, there are two reasons. One is that when freshly power up, the power supply is loaded by some other circuit which drops the volatge below the microcontrollers minimum level. Reson two says that the said LCD is not compatible with your hardware. Just use other brand and post the results.
Cheers

rectified the problem , I put the 1k resistor between controller tx and mcp2200 rx , and 1k resistor between controller rx and mcp2200 tx , ground is common , worked ............Now wen i power on the system with usb cord being already plugged in to laptop , The lcd initializes properly............

many LCD controllers require stable power supply before initialisation.
In our circuit we use bulk capacitor for ripple rejection on power lines which takes time to charge
every LCD manufacturer specifies time for stable supply...
when you reset ur controller the power has already is stable & by resetting controller you are just reinitializing the LCD by mean of ur code...
try providing sufficient delay before LCD initialization or simply call LCD_INIT() function twice, back to back....