inverted TTL == negative logic ??

[hani_a]

Hello people,

does anyone know for sure if inverted TTL means negative logic? if not, can one explain to me what inverted TTL..

Thanks!

 

[Nigel Goodwin]

Hello people,

does anyone know for sure if inverted TTL means negative logic? if not, can one explain to me what inverted TTL..

Thanks!

It depends on the context, if low is a '1' and high is a '0' then that's inverted logic - but in many TTL circuits this will occur at various points within the circuit anyway.

I would only consider it negative logic if the entire design worked that way.

 

[weegee]

if this is in response to the other post then inverted TTL is the output from a microcontroller for controlling serial devices, so when something is sent from the controller to the recieving device - the signal is the opposite of what a full RS232 serial device would show - eg a '1' on RS232 is actually -12v, and a '0' is +12v, although if you are dealing with inverted TTL in this sense a '1' is +5v and a '0' is 0v - This is the way that many serial devices work to negate the effect of having to use MAX232 ect. to provide the +12v and -12v for full RS232 spec.

I hope that makes sense to you :?

 

[FJSchrankJr.SMCO]

weegee is exactly right.

Many times with mcu's such as the PIC Micro you will see that you can drive a serial port directly from the mcu's pins if you use inverted TTL as opposed to using a level converter (like weegee mentioned, MAX232). Make sure to use current limiting resistor(s) though.

For example: If you wanted your PIC 16F84 to send data back to a PC you only need 2 wires, Ground (RS232 DB9 PIN 5) and RX (RS232 DB9 PIN 2) with a 1k resistor between your PIC port and RX serial line and inverted TTL.

and if you want to send data from your PC to PIC, use the TX line then with 22k resistor and inverted TTL.

or for bi-directional communications, 3 wires: TX (w/22k resistor), RX (w/1k resistor) and GND.

if this is in response to the other post then inverted TTL is the output from a microcontroller for controlling serial devices, so when something is sent from the controller to the recieving device - the signal is the opposite of what a full RS232 serial device would show - eg a '1' on RS232 is actually -12v, and a '0' is +12v, although if you are dealing with inverted TTL in this sense a '1' is +5v and a '0' is 0v - This is the way that many serial devices work to negate the effect of having to use MAX232 ect. to provide the +12v and -12v for full RS232 spec.

I hope that makes sense to you :?

 

[colin55]

Inverted TTL simply means any HIGHs are converted to LOWs and any LOWs are converted to HIGHs.
If you mean Negative Logic, it means a single LOW or multiple LOWs will turn on a particular device or create a HIGH output from a gate or in some way have an effect on the next "building block."
As the other replies suggest, you need to give more details to get a definite answer.