Micromite RS232 interfacing

Dear oh dear! Don't trust this person if you want a design that works!

If you connect TTL device to an RS232 device you will have a logical inversion problem.

I'm not sure what TTL device you are proposing to connect to an RS232 device.

I thought you were going to connect a Micromite to an RS232 device, and in that case the "inversion" problem may be trivial to solve. At least that is according to the creator's Micromite Manual where in the "Low Cost RS-232 Interface" section it says that COM1 can be opened with a parameter to invert the output.

I think the OP wants to use the PC to program the Micromite, which involves communicating with it before being in a position to tell it to invert the output.

Sylvia.

You've got a serious head-up-arse problem there mate.

read what I wrote.

Ah, I missed that, but perhaps you are right (assuming that PIC has some bootstrap serial programming capability - I wouldn't know as I have not done anything with a PIC for over a decade).

You won't get a Micromite console port talking to a PC's COM port unless you invert the voltage. Fact is, TTL logic ONE is positive, RS232 logic ONE is negative.

It's not a virgin PIC. A third-party supplier pre-programs it to support a variant of BASIC.

Sylvia.

The Micromite is a pre-programmed PIC32. It has been programmed with a Basic interpreter and communicates via a serial interface, so you need a PC terminal emulator such as Tera Term. The Micromite uses the TTL logic convention for it's console serial interface, so you need to use either a USB-TTL adaptor or an RS232-TTL interface (which inverts the voltage) to connect it to a PC.

Read the subject............

An ideal thing for a script kiddie.

Lay off the booze, it is showing in your nonsense ...

A TTL positive can mean anything. The logic of what a device outputs using TTL levels is determined by the DEVICE, not by a particular convention.

You won't get a Micromite to talk to PC's COM port if don't invert the signal. The convention with serial comms is for a TTL logical ONE to be a positive voltage. Read the SUBJECT.

I quite believe that, having not played with them.

I did.

But you went all extravagant when you claimed:

and that ("always") is simply NOT TRUE.

It was true when RS232 comms dominated, although we are getting into ancient history. "Always" applied when micros operated at TTL compatible levels but RS232 was the standard I/F. It was the convention for the TTL logic to be the opposite voltage when RS232 was THE serial I/F. In my experience, programmers wrote serial communication routines expecting the logical ONE in their software to be output as a TTL logical ONE, i.e positive. When you wanted an RS232 I/F you added an inverter or a MAX232-style chip. Put it down as a history lesson.

It was the more common practice, but far from "always"

If the TTL logic were positive then obviously an inverting level shift to/from RS232's inverted logic. No argument there.

I've been there (creating custom interfaces to/from RS232 devices) for probably a bit over thirty years. The issue with RS232 as a standard was that it was cited far more often than followed.

Put it down to learning to be less dogmatic in your claims.

Almost always ;)

see:

At least one user now has a real RS-232 port running the MicroMite.

Cheers Don...