Micromite RS232 interfacing

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Has anyone here used the Micromite 28DIP to connect to the standard PC  
COM1/2 RS232 port?
The Micromite is described in Silicon Chip, but there are no wiring  
diagrams that show you how to connect it to a PC COM1/2 type RS232 port,  
as found on older PC's.

I suspect you have to invert the voltage levels, as they recommend using  
a USB/TTL converter. TTL levels are always inverted wrt RS232.
So if you want to conect a Micromite chip to your PC you will have to  
invert the logic levels on the Micromite console port.



Re: Micromite RS232 interfacing
On 17-Jun-14 10:54 PM, Yaputya wrote:
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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:
http://www.thebackshed.com/forum/forum_topics.asp?FID16%&PN=1


Cheers Don...


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Re: Micromite RS232 interfacing
On 18-Jun-14 7:24 AM, Don McKenzie wrote:
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see:
http://www.thebackshed.com/forum/forum_posts.asp?TID67%01&PN=1

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

Cheers Don...


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Re: Micromite RS232 interfacing

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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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Re: Micromite RS232 interfacing
On 18-Jun-14 8:41 AM, Computer Nerd Kev wrote:

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

Cheers Don...




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Re: Micromite RS232 interfacing
On 18/06/2014 12:41 AM, Computer Nerd Kev wrote:
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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.



Re: Micromite RS232 interfacing
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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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Re: Micromite RS232 interfacing
On 18/06/2014 2:12 PM, Jasen Betts wrote:
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The formal 'RS232 spec.' does say the level between -3V and +3V is  
undefined.
http://en.wikipedia.org/wiki/RS-232

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.



Re: Micromite RS232 interfacing
On 17/06/2014 10:54 PM, Yaputya wrote:
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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:

https://www.dropbox.com/s/zp0vkwiscuawmxc/serial.png

Sylvia.

Re: Micromite RS232 interfacing
On 18/06/2014 3:18 AM, Sylvia Else wrote:
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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.



Re: Micromite RS232 interfacing
On 18/06/2014 3:49 PM, Yaputya wrote:
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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.

Re: Micromite RS232 interfacing
On 18/06/2014 8:37 AM, Sylvia Else wrote:
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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.
http://www.picaxe.com/docs/picaxe_manual1.pdf

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.



Re: Micromite RS232 interfacing
On 18/06/2014 9:21 PM, Yaputya wrote:
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Even some current motherboards have a RS232 header, just not a back  
panel socket.

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

Sylvia.

Re: Micromite RS232 interfacing
On 18/06/2014 2:33 PM, Sylvia Else wrote:
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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.


Re: Micromite RS232 interfacing
wrote:

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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.

Re: Micromite RS232 interfacing
On 18/06/2014 5:11 AM, pedro wrote:
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You ALWAYS have to invert TTL to get RS232.

Re: Micromite RS232 interfacing
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the PIC is CMOS.

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


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umop apisdn



Re: Micromite RS232 interfacing
On 18/06/2014 2:26 PM, Jasen Betts wrote:
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You always have to invert TTL to get RS232.
A logic 'one' is a positive voltage in TTL and a negative voltage in RS232.
http://en.wikipedia.org/wiki/RS-232



Re: Micromite RS232 interfacing
On 19/06/2014 7:22 AM, Yaputya wrote:
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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.



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Re: Micromite RS232 interfacing
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point 1:
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point 2:
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see point 1.
that doesn't make logial sense.

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see point 2.
It says you're wrong too. (most recent edit 14 May)

If you were to say "UART" instead of "TTL" you'd be right,

TTL is mainly a voltage level standard  2V or more is high, 0.8v or
less is low,  those levels are compatible with the 1487 RS232 reeiver  

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