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RS-232 communication between 2 PCs in comparison to one with PC and MCU

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Full Member level 5
Oct 22, 2005
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I noticed the following. Connecting 2 PC's together serially (RS232) u twist the cable. However communication between my PC and a MAX232->MCU uses a straight cable.

Why is this?

My reasoning is that tieing Tx(PC) to Tx(MAX) would result in collisions as both pins/lines are transmitting data?

Any ideas?

Re: RS-232 Communication

How Can I Identify DTE or DCE Type Connections?

What devices have DTE type RS-232 ports? A DTE device is "Data Terminal Equipment", this includes Computers, Serial Printers, PLC's, Video Cameras, Video Recorders, Video Editors, and most devices which are not used to extend communications. Think COMPUTER for DTE.

What devices have DCE type RS-232 ports? A DCE device is "Data Communications Equipment", this includes devices intended to plug directly into a DTE port, PDA cables, Modems and devices that extend communications like a modem, such as RS-422, RS-485, or Fiber Optic converters or Radio Modems. Think MODEM for DCE.

Rule of Thumb: When connecting a DTE device to a DCE device, match the signal names. When connecting two DTE or two DCE devices together, use a crossover cable. (TD crosses to RD, RTS to CTS, DTR to DSR as shown in Modem to Modem connections)

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Re: RS-232 Communication

actually you are connecting the tx of pc to the rx of the mcu and viceversa
seethe diagram of your max 232 to the mcu
if it's not so,the communication will not take place


Re: RS-232 Communication

Slayerza said:
as both pins/lines are transmitting data?

TX has the ambiguos name of transmitted data, which you could refer to either side of the connection because both are transmitting data.
For this line you should always take the point of view of the DTE device, which is usually the terminal or PC you will be working on. So, TX referrs to data that is being transmitted from your PC. RX refers to data that is being received by your PC.

My 2 cent advice.

- Never relies on marked lines.
- Don't try to figure out which is which, DTE or DCE (how about two microcontrollers communicates through serial lines; obvious they are both DTE)
- Allways use a DC voltmeter and measure the DC level of the involved pins as described in page 5 of document mentioned by IanP

Re: RS-232 Communication

Just make sure that Rx of one uC is connected to Tx of another and viceversa.

Re: RS-232 Communication

The case is the direct use between transmitter and reciver you plug the TX of the transmitter and RX of the transmitter to the TX of the receiver
But connecting it to any external device you may twist the i/p as they are inverted at the reciver

RS-232 Communication

i need the data sheet of max232 and max233,anybody can help me?

Re: RS-232 Communication

i think you know the different pins on rs232.

2nd pin is the tx pin.3rd pin is the rx pin .as far as i know inorder to connect two PC's serially it doesn't need a mcu or any external hardware .As the Pc itself contain UART and MAX level converter.So what we need to do is just interconnect the 2nd ,3rd pin wires an one end that all what it needs

try it i am sure it will work

all the best

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