TTL input - 3rd states possible?

[flotulopex]

Hello,

I was asking myself about the possibility of using any TTL input of my PIC to "read" 3 different levels.

Roughtly, for TTL values, the LOW level is from 0V to 1V and the HIGH is from 3,5V to 5V.

Assuming this is not completely wrong, would it be possible to read 3 different states on the PIC?

I tried to make it a simple way with a 2 resistor divider between Vdd and Vss. The middle point of the divider is logically connected to the pin.

Two buttons are parallel connected each to a resistor.

In theory, I can simulate 3 states:
1.- 0V (if button "A" is pressed)
2.- something around 2V (no button is pressed)
3.- 5V (if button "B" is pressed)

I can't achieve to read state 2.- but is it really possible... or am I dreaming?

[skimask]

Hello,

I was asking myself about the possibility of using any TTL input of my PIC to "read" 3 different levels.

Roughtly, for TTL values, the LOW level is from 0V to 1V and the HIGH is from 3,5V to 5V.

Assuming this is not completely wrong, would it be possible to read 3 different states on the PIC?

I tried to make it a simple way with a 2 resistor divider between Vdd and Vss. The middle point of the divider is logically connected to the pin.

Two buttons are parallel connected each to a resistor.

In theory, I can simulate 3 states:
1.- 0V (if button "A" is pressed)
2.- something around 2V (no button is pressed)
3.- 5V (if button "B" is pressed)

I can't achieve to read state 2.- but is it really possible... or am I dreaming?

You can do 3 states with a regular ol' TTL pin right now, but it takes a bit of programming.
1 and 0 are self explanatory, set the pin to an input and read it...
then you can read the 3rd state...open...
set the pin to an output, output a 1, read the input back...if it's a 0, it's being held to a 0 (in other words, not open), then set the output to 0, read the pin back, if it's a 1, it's being held to a 1 (again, not open)...however if you read back exactly what you put out, then the pin can be reasonably assumed it's open.

But the way you described works well too, if you're using a button sort of thing.

[Luciano]

Hi,

See tip #3:

http://ww1.microchip.com/downloads/e...doc/40040b.pdf

Best regards,

Luciano

[flotulopex]

Thanks to both of you,

The Tips & Tricks documentation is cool :-)

I'll have a try with tis stuff.

[flotulopex]

Well,

After a few hours trying to get a positiv result, I just got nothing working.

I would like to read two buttons connected to one pin.

The states are "0" and "1". The third "Z" state is not relevant to me here.

To make sure I have an intermediate level, I use a 2 resistor divider like described in the first post.

Currently, I can't get clear "0" or "1" states.

Any idea?

OSCCON       = %01100000  '4MHz
OPTION_REG   = %10000000  'D I S A B L E PORTB's Pull-Ups for buttons
ANSEL        = %00000000  'Disable Analogue Inputs
TRISB        = %00010000  'Inputs/Outputs
PORTB        = %00000000  'Drive all ports low

MAIN:
    IF PORTB.5 = 0 THEN PORTB.0 = 1
    IF PORTB.5 = 1 THEN PORTB.1 = 1
    PAUSE 1000
    PORTB.0 = 0
    PORTB.0 = 0
    Goto MAIN
    end

I use PORTB.5 of my PIC16F88 for buttons because it is a TTL input only.

[paul borgmeier]

TRISB        = %00010000  'Inputs/Outputs

you have PORTB.4 set as input, not PORTB.5