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RS-485 standard with USB

joniengr

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Hi,
I am wondering which cable and which connector do we normally use for RS-485 standard. Is it possible to convert RS-485 to USB like we do in case of RS 232 ?

Can we use pin 8 and pin 9 of DB 9 for RS 485 ?
 
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00kam

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hello
you can convert RS485 to USB .RS485 use for long distance(industrial application) to transceiver the data the cable used in RS485 is twisted pair cable(two wire) . regarding the pins 8,9 of DB9 connector that depends in you design .there is already adapters conv. from RS485 to USB

kamal
 

joniengr

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Hi,

Is it possible to use TeraTerm terminal or PuTTY to read RS 485 data in PC ? Does it also work with +/-15 Volt on PC side ?
 

00kam

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hello
first thing does your P.C has RS485 port to configure PuTTY works with RS485 ? i think the answer is NO but if you say RS232c port i guess yes maybe only in the old disktop P.C but modern lap doesn't has . so you have to have a converter adapter RS232 or RS485 to USB . the converter software driver works as "VCP" Virtual COM Port Drivers but the interface port(hardware) in reality is USB .
regarding with level voltage +15/-15 on P.C side only if your P.C has RS232 com port hardware. in this case you have to use" MAX232c" I.C to converter level from UART device to P.C and from P.C to UART

kamal
 

betwixt

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RS485 is NOT a data protocol, it defines an electrical specification. The data it carries is just plain ordinary serial bits. As long as you convert the RS485 signals to/from appropriate unipolar logic levels it can be produced/read by any serial port.

It normally works with +5 between the two signal wires (sometimes 3.3V is used) but the polarity is reversed to carry the '1' and '0'. As the voltage polarity between the two wires carries the data, it doesn't need a perfect ground as a reference provided the actual voltage remains within the limits allowed by the transmitting and receiving devices.

Brian.
 

joniengr

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We can use DB 9 connector for UART both electric signal standards (RS 232 and RS 485). Can we use serial PuTTY terminal for both RS 232 and RS 485 ?
Which connector do we use for RS-422 which has differential signalling ?
 

betwixt

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Again RS485 (and RS422) are NOT protocols. They are electrical specifications and nothing to do with the data they carry.
If converted back to serial data and at appropriate voltage levels they can be read by PuTTY or any other serial terminal through a UART.

Brian.
 

reza147

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Hello
In digital systems, information is generated as bits of zero and one per transmission; The data packet, the number of constituent bits, the beginning and the end of the data are specified as a set of rules or protocols between the sending and receiving devices. Each system can achieve the meaning of data by processing the number of bits of zero and one.
In order for separate circuits to be able to exchange information with each other, they must use a common rule or protocol, this information transfer or data transfer can be done in series or in parallel. Data transfer may take place between a computer, device, microcontroller or other equipment.
So keep in mind that each of Protocols 232 and 485, 422 or USB follows the property rules, and you ca
 

00kam

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Hello
In digital systems, information is generated as bits of zero and one per transmission; The data packet, the number of constituent bits, the beginning and the end of the data are specified as a set of rules or protocols between the sending and receiving devices. Each system can achieve the meaning of data by processing the number of bits of zero and one.
In order for separate circuits to be able to exchange information with each other, they must use a common rule or protocol, this information transfer or data transfer can be done in series or in parallel. Data transfer may take place between a computer, device, microcontroller or other equipment.
So keep in mind that each of Protocols 232 and 485, 422 or USB follows the property rules, and you ca
RS232 , RS485 , RS422 and USB are not Protocols those are interface port (connectors) each one has electrics chararcteristics .RS232 is used for short distance (over 15 meter and depends on baud rate ) with level voltage +-/15 volt . RS485 is used for long distance (you can say more than 100 meters ) with low level +-/5 voltage half duplex . RS 422 is used for very long distance over 1 km full duplex . if you want to know what are half duplex , full duplex just post
 

KlausST

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Hi,
So keep in mind that each of Protocols 232 and 485, 422
I can just repeat what Brian said twice: RS232, RS485, RS422 are no protocols.
Example for a protocol: MODBUS. It may run on RS485.
PROFIBUS may also use RS485, but uses a different prococol.

But USB specification includes a protocol.

Klaus
 

betwixt

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... And those distances figures are silly.
Perhaps you can explain the difference in achievable distances 00Kam, in particular why you think RS485 and RS422 are so different.

Brian.
 

00kam

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... And those distances figures are silly.
Perhaps you can explain the difference in achievable distances 00Kam, in particular why you think RS485 and RS422 are so different.

Brian.
you may consider this link silly
kamal
 

betwixt

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That web site is full of wrong information, not only the achievable distances but the topology and signalling too. Even the 'data structure' diagram is wrong and implies the clock is part of the RS-xxx specifications. The only time the clock is transmitted is in synchronous RS232 which is hardly ever used, I don't think I've ever seen it being used and I've been in the electronics business more than 50 years!

The achievable lengths is largely determined by the type and quality of cable but RS232 can easily reach 200m even at quite high speeds.
RS422 and RS485 are electrically virtually identical and can drive up to about 1.5KM at very high speeds. RS485 uses two wires for transmission and reception so it needs a control mechanism to decide which way the data is to flow, RS422 uses four wires, two for transmission and two for reception so it can work full duplex. There are limits on the number of listening devices on RS485 and RS422 because of the loading effect of their receivers and to some extent the number of addresses that can be accessed if 9-bit mode is used.

Brian.
 

reza147

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Hello
In digital systems, information is generated as bits of zero and one per transmission; The data packet, the number of constituent bits, the beginning and the end of the data are specified as a set of rules or protocols between the sending and receiving devices. Each system can achieve the meaning of data by processing the number of bits of zero and one.
In order for separate circuits to be able to exchange information with each other, they must use a common rule or protocol, this information transfer or data transfer can be done in series or in parallel. Data transfer may take place between a computer, device, microcontroller or other equipment.
So keep in mind that each of Protocols 232 and 485, 422 or USB follows the property rules, and you ca
Hi
Yes. I apologize. Wrong. 485, 232 and 422 are not protocols, but a physical layer for some protocols.
 

KlausST

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Hi,

Especially with UART, USART, RS232, RS485 and so on there is so much wrong information around.
We really should try to post valid informations.
We won't be perfect, but we should try to come close to it.
And we should not fight against each other, let's focus on the technical part.

There is no exact value for distances.
It depends on many things.
* there is a big range of valid driver level voltage
* baud rate
* voltage rise/fall rate
* receiver input levels
* cable type
* noise in environment
...

Klaus
 

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