Unable to use PORTE as analog input

[cxiong]

I try to use PORT E as Analog input. I can't use any of PORT E for
Analog input. I want to use PORTE because I have the
PIC Demo 2 plus board and RA0 already connected to
a POT, A1-A3 are connect to the LCD control signal. I try to connect
a thermistor to RE0, but there is not useable, when I use
the switch ALL_ANALOG then it screwed up the LCD.
I want to leave PORT for the LCD and use porte for
the analog.

Please help!!!!

[PCM programmer]

Of course you didn't tell us what PIC you're using, since we are
mind readers. And also the compiler version.

So I'll assume a 16F877.

Get the data sheet from Microchip for the 16F877.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2046

In section 11.0 of the data sheet, look at the chart for the ADCON1
register. It lists all possible settings for Port A and Port E.

Then look at the 16F877.H file in your text editor. This file is found here:
c:\Program Files\Picc\Devices
Find the section called: Constants used in SETUP_ADC_PORTS()
Then find the constant defined by CCS that matches the configuration
that you picked from the chart in the data sheet. Then use that
constant as a parameter when you call the setup_adc_ports() function.

That's how you do it.

[cxiong]

I use the PIC18F458 and I did look at the device file the CCS
defined the constant. None of them match what I need.
Either set ALL_ANALOG OR most of the constant just for
PORTA.

Here I copy it from the CCS file. Which one is the right one
for setting PORTE RE0, RE1, RE2 to analog:

[PCM programmer]

The Port E and Port A settings are shown in the 18F458 data sheet in
Section 20. The chart shows that you can't set Port E to be analog pins
just by itself, while keeping Port A as digital.

This is a limitation of the PIC hardware. You will have to re-design
your external circuit so it will work with the Port A and Port E settings
that are listed in the data sheet.

[treitmey]

Are you trying to use the TC74 in position U5 on the PICdem2 plus board?

[cxiong]

I add more thermistors into the demo board, and I also
add a low voltage detector circuit to the demo board to monitor the
9V battery. I run out of Analog I/O due to RA1 - RA3 tied to
the LCD on the demo board. That's why I try to use PORT E.

[rnielsen]

The best thing to do is to download the spec sheet, from Microchip, and look what configurations are possible. From what I could see if you want to use AN5, AN6 or AN7 (PINS RE0, RE1 and RE2) all of PortA will need to be set as analog pins as well.

Ronald

[Mark]

Here is a hint:

A pin can be an analog input in one part of the code and an output in another part of the code provided the changing doesn't affect the LCD.