[b3lha]

Originally Posted by cdvs

For those that don't know UART is Universal Asynchronous Receiver Transmitter. It refers to the hardware device used to implement RS232 which is the engineering standard for asynchronous comminications.

TTL levels are +5 to -5 and fall within the RS232 spec. AFAIK, the only reason to use higher voltages is to overcome line losses that occur over long distances. This is not an issue here.



What this simple circuit adds are always on request to send and clear to send signals. These signal lines were incorporated to overcome a devices processing limitations. This became a non-issue around 1970 and are rarely, if ever, used today. Anyway, what this stuff does is defeat their purpose. Something akin to fingernail polish. It might look good and doesn't hurt anything, but serves no useful purpose.



I'm not out to prove anything. I was attempting to make a contribution. I would have preferred to test this, but I don't have the time. I'm over-indulging my interest just making these posts. Someone else will have to carry the ball from here, or not.

Charl

OK. You obviously know about electronics than I do. I welcome your contributions to this thread.

I don't understand what you mean about RS232 and TTL voltages being compatible. In the data sheet for the M377xx CPU, it specifies the "Absolute Maximum Ratings" for the inputs for the UART pins as -0.3 volts to Vcc+0.3 volts. Vcc being 5 volts.

Would it not exceed the maximum rating by a factor of over 100% if your PC serial port supplied a 12 volt signal to these pins?