On Fri, 04 Mar 2011 21:53:42 -0000
"al_martinez" wrote:

> I have an Atmega 128 and read the manual. On page 180 the information
> given does not include whether the transmission signal sent out of
> the TXD pin (3) is inverted or non_inverted.
>
> I know the default transmission settings are 8N1 9600 baud, but I
> need to verify if it is inverted or non_inverted.

As usual, non inverted (idle is VOH).
>
> Also, If I use the chip for only transmission, do I need to ground
> the receive RXD pin (2) or do I need to connect that to the other
> chip as well?

I'm not 100% sure but I think you can use it as a general purpose input
if you want.

>
> Thank you in advance for your response
>
> Al
>

hi,
normally, TXD = 1, when Mcu transmits a byte, it start with START Bit = 0, Data Bits are as you send them, then STOP bit = 1
that's mean the MCU sends 10 bits : " 0 , [8 data bits] , 1 " in your case.

if you use a TTL to RS232 interface (as MAX232, MC1488, ...) it converts the logical one to
-8V {-5 .. -20V ok} and the logical zero to +8V {+5 .. +20 OK}, which you find on pin 3 of 9 pins PC Com PORT.

From: al_martinez
To: a...
Cc:
Sent: Friday, March 4, 2011 11:53 PM
Subject: [AVR club] Atmega 128 USART TXD info

I have an Atmega 128 and read the manual. On page 180 the information given does not include whether the transmission signal sent out of the TXD pin (3) is inverted or non_inverted.

I know the default transmission settings are 8N1 9600 baud, but I need to verify if it is inverted or non_inverted.

Also, If I use the chip for only transmission, do I need to ground the receive RXD pin (2) or do I need to connect that to the other chip as well?

Thank you in advance for your response

Al

Steven,

Thank you for your answers.

Al

On 04/03/2011 21:53, al_martinez wrote:
>
> I have an Atmega 128 and read the manual. On page 180 the information
> given does not include whether the transmission signal sent out of the
> TXD pin (3) is inverted or non_inverted.
>
> I know the default transmission settings are 8N1 9600 baud, but I need
> to verify if it is inverted or non_inverted.
>
> Also, If I use the chip for only transmission, do I need to ground the
> receive RXD pin (2) or do I need to connect that to the other chip as
> well?
>
> Thank you in advance for your response
>
> Al
Hi,

No the output is not inverted, as usual for a uart the tx line is held
high when idle, if you don't need to use the rx line then do not enable
it in the UCCRB Register, you can use it as a standard i/o pin.

Regards

I have an Atmega 128 and read the manual. On page 180 the information given does not include whether the transmission signal sent out of the TXD pin (3) is inverted or non_inverted.

I know the default transmission settings are 8N1 9600 baud, but I need to verify if it is inverted or non_inverted.

Also, If I use the chip for only transmission, do I need to ground the receive RXD pin (2) or do I need to connect that to the other chip as well?

Thank you in advance for your response

Al