Micromite RS232 interfacing

correct.

You would basically need an RS-232 to TTL converter board to make it work from a standard PC RS-232 com port. Even then, I haven't heard of anyone yet doing this. There may be something in the very active usergroup archives at:

Cheers Don...

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Don McKenzie 

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I've never done anything with RS232, but I think the MAX232 chip might be what you're after.

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yes, the converter board would have a MAX-232 or equiv.

Cheers Don...

-- Don McKenzie

All Olimex products now 30% to 90% off normal Olimex Prices.

Many other items discounted up to 90% off. Also discounts on FTDI, Sparkfun, mELABS, CCS, SimmStick, etc.

The Micromite is PIC32 device.

I haven't linked a PIC32 to a PC serial port, but I have done for PIC16 and PIC24 devices, which raise the same issues.

I've used this configuration with success:

Sylvia.

Not strictly true. There are a number of cases where RS232 polarity signals with (only) TTL levels are presented. In *most* such cases, direct connection works fine. When in doubt, check.

You ALWAYS have to invert TTL to get RS232.

Yeah, I've got a few MAX232's somewhere. But you can also just use transistors to invert the signal. You can even 'pinch' a negative voltage from the host RS232 interface's RXD pin via a diode-cap since it sits at MARK or negative volts most of the time. Most RS232 devices work fine with just zero volts as MARK though.

Thanks, no doubt that circuit has worked well. However, you don't really need to connect to the RS232 DTR pin, you can use the host micro's Vdd pin if it is over 3V.

In practice, probably, and of course the 0V level is not strictly valid either. Still, using DTR takes the 1 level further away from RS232's limits.

Sylvia.

Probably the easiest way to get a 100% true-blue RS232 interface is to use a MAX232 style chip, but it ain't strictly necessary.

I've never had a problem connecting PICAXEs to COM ports with the standard RevEd interface, this works because the RS232 minimum is supposedly +/- 3V, but in the real world 0V and 3V works fine. See page 44 here: Note - they consider RS232 to be OBSOLETE!!! - I'm sure many electronic hobbyists still use 'legacy' PCs in their garage/cellar.

A minor advantage of using the micro's Vdd is that you only need three wires in the I/F cable (if you put the inverting transistors on the micropocessor end).

BTW Have you tried out the Maximite/Micromite? I've got one on order.

You don't actually need the negative voltage to have somethig functional, especially on short cables.

it's needed to be within spec, but no actual rs232 receivers need to see anything lower than +0.5V to register a "mark"

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the PIC is CMOS.

(No, you don't) ((like I said))

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Even some current motherboards have a RS232 header, just not a back panel socket.

No - I've just used the Microchip software development tools in C and assembler, so not had to buy pre-programmed controllers.

Sylvia.

Please re-read what I said before getting your knickers in a twist.

The VOLTAGE is inverted - a TTL positive is an RS232 negative.

You always have to invert TTL to get RS232. A logic 'one' is a positive voltage in TTL and a negative voltage in RS232.

Strictly speaking, the Picaxe is not an interpreter as only a small set of routines are pre-programmed, the rest is compiled when you download. I have hardly used assembler since the 8048/8052 Intel micros - no need any more as the modern micros have become powerful enough to run compiled code at a reasonable speed. Of course you will always get the fastest operation with assembler, at the expense of programming development time. I've got an old Intel 8052AH-BASIC chip that has an onboard 8K ROM Basic and allows you to call machine code subroutines - the best of both worlds.

The formal 'RS232 spec.' does say the level between -3V and +3V is undefined.

In the real world this isn't the case, as the success of the simple Picaxe RS232 interface shows. I've downloaded programs from a PC COM port to a Picaxe powered by just 2.4V.

And just in case you don't know it, both TTL and CMOS have logic one as positive voltage. So you need to invert it for RS232.