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Author Topic: rs232/usart  (Read 1655 times)
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wop
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« on: June 02, 2006, 11:17:28 11:17 »

So I am using an hcs12 and trying to communicate to another device using a usart. i have noticed that i must connect the transmit line of the usart to the transmit line of my rs232 level shifter to get things to display on my computer, why is this?

thank you.
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donat
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« Reply #1 on: December 05, 2007, 06:46:57 18:46 »

this is because the max 232 is as you say a level shifter, it just upps the levels.

The tx and Rx lines should be mixed from the rs232 to the PC.

Greets. D.
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computer
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« Reply #2 on: December 11, 2007, 10:06:10 22:06 »

The level shifter must convert the TTL signal from the HC12(0V for logic 0 and 5V for logic 1) to the computer's RS232 standart signals(12V for logic 0 and -12V for logic 1).

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yoda
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« Reply #3 on: December 14, 2007, 12:27:13 00:27 »

i have noticed that i must connect the transmit line of the usart to the transmit line of my rs232 level shifter to get things to display

Hello,
The TX and RX indications are given to I/O lines following the RIAA or RS232 specifications for DB25 connectors, which are male and female (of course) and in some situations don't reflect the actual data direction, which can be confusing.
Bye
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pici192
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« Reply #4 on: December 21, 2007, 02:13:54 14:13 »

Are you think on this?:
http://www.sprut.de/electronic/pic/grund/rs232.htm
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pinoytsikboy
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« Reply #5 on: December 22, 2007, 04:25:12 04:25 »

Hi. if you are into microcontrollers, some of them has built in TX/RCV for RS232. no need for level shifters. PIC 16f87xx series and some 18Fxxx are examples.
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yoda
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« Reply #6 on: August 07, 2008, 11:54:43 23:54 »

Hi. if you are into microcontrollers, some of them has built in TX/RCV for RS232. no need for level shifters. PIC 16f87xx series and some 18Fxxx are examples.

Is that true? You should connect + and - 12v. to the chip then, or are there switchers inside like in the Maxim 232 chips?
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sunskier
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« Reply #7 on: August 12, 2008, 08:06:54 08:06 »

Sorry, I don't think so. First, i am a newbie learn'n pic.
But, there always has max232 chip between pic and rs232.
If you connect +/-12v to pic directly, it'll burn.   Sad
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yoda
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« Reply #8 on: August 13, 2008, 12:01:44 12:01 »

Hi. if you are into microcontrollers, some of them has built in TX/RCV for RS232. no need for level shifters. PIC 16f87xx series and some 18Fxxx are examples.

Only if you connect on logic level (ttl) you can leave out a level shifter IC. But then you should'nt call that RS232, because that implies using + and minus voltages.

So you can definitly not connect a 16F87 chip without a levelshifter (max232) to an RS232 device, cause the PIC is all ttl only.
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