AVR Freaks

A Usart signal idles high, I would place a pull up resistor 10k on the rx line to hold it high while the toggle switch is changing from one tx line to the next.

see if that helps.

jim

 

Wouldn't life be a whole lot easier if you simply based your design on an AVR that has the number of UARTs that your design actually calls for rather than trying to shoe-horn everything into the single UART that the mega8 has? Things like mega324P/644P (40 pin DIP) for example have a couple and a lot of the newer AVR-0/AVR-1 type device have lots of them.

As you have the wrong sequence and numbers of the correct bytes,

you likely have a logic error in how you handle correct data.

By any chance do you read the tag more than once to check for errors?

 

Do you mean tat you are already using all the pins on the chip so that there are non left for "soft UART"? if the soft UART is going to be transmit only (usually a good choice!) then you only need one GPIO pin. If you want receive as well it would need two port pins.

 

And the point I make here is valid. To "fake a UART" it's actually pretty easy to get the transmit part working with the correct timing but reception can be a real problem as it could happen at any time. So if you have two UART attached devices but for one the AVR only sends to it (like sending debug messages to a PC say?) then elect to do that one with softUART and keep the real UART for the thing that may also transmit to the AVR

As I said earlier the "best" solution is to pick the right micro for the job. If you can trade up from a mega8 to something like a mega164P you will have 2 UART anyway.

It's a bit like saying I want to get from Los Angeles to New York but I've only got this bicycle. Life would be a lot easier if you bought a Ferrari! ;-)

Why do you post a million one sentence answers??   Post only full paragraphs so people can understand you.   This is a conversation, not a bunch of sound bites.

 

Take all of the following & turn it into some sort of commentary & explanation---it will be more sensible to everyone.

 

Thank you i will use 16Mhz external osc.
I am using toggle switch for two peripheral device. Is it correct?
Yes, i was simulate the circuit in Proteus ISIS. Circuit is running correct in the simulation. But running incorrect in the real (bread board)
I tought that, but firstyl i want solve the problem with in my hand mcu. In worst case, i will do that.
I heard that, can i imlement softuart library for ATmega8A beacuse ATmega8A is haven’t general porpose pins.
Yes i am reading tag more than. What kind of logic error could it be?
Yes i have two signals. Thank you i will try that.
I saw them, i will try them as soon as.
I downloaded the softuart, I will try it after trying other solutions. Thank you.
I thought but I want to do with the MCU in my hand. Thank you for your suggestions.
Yes you are right :) if i make this i will send reply here thank you for your replies

You can multiplex one USART TX pin to two devices with only two resistors...

 

 

Set the associated EN pin as a high output to disable the feed to that external device. Set it as an input to enable that device.

BTW, the above two posts are a complete hack and are only there as a way to get you out of a hole. There are lots of problems to get them to work properly and lots of reasons why they won't always work.

 

The proper way to do it is either...

 

a) Use a chip with two USARTS or

b) Use an external chip to do the multiplexing.

If you have full control of all of the devices (your code in each), you can designate the main unit as the master....all other units listen at all times, only one can TX back to the main unit at a time, upon query from the master (rquest voltage reading, sensor reading, etc)

The units that are not transmitting back, put their TX pin in high-Z state.  A few resistors are needed such as pullups & separation resistors are a good idea too.  This works nice when the devices are "widely" separated by a few feet & perhaps you need to talk with 5 different devices.

A more robust method is to use rs485 or similar hookups...then you can go hundreds (or more) feet.