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"RS-232 port to transfer data to PC for analysis"

joniengr

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Hi,

I am looking for thermocouples with readers. I just found one with software support. There is a statement in the user manual / datasheet. I am trying to understand this statement.

"RS-232 port to transfer data to PC for analysis"

Using RS-232 port to transfer data to PC means that the serial communication protocol is UART ? Is it possible to use RS-232 port for another protocol ?
 

KlausST

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Hi,

RS-232 is mainly a definition of timing and voltage levels. It is an interface description.
It is not a true protocol.

a UART is an interfce (IC) that mainly does the parallel-serial and serial-parallel shifting and generates the timing.
UARTS usually output either
* 5V TTL levels
* 5V CMOS levels or
* 3.3V CMOS levels
.. and they generate the timing.

A true protocol defines the meaning of the sent data. It describes Tx- and Rx- frames, CRC, and the timing (frame, response) and so on.

*****
We don´t know anything about your device.
--> please post a link to the datasheet.

But it seems the device has an internal memeory for storing measurement data and an RS-232 compatible interface to communicate with the PC.
You need to have a dedicated PC software, or at least a decription about the UART setup (baud rate, handshaking...) and the communication protocol.

Klaus
 

joniengr

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It is Extech EA15 Dual Input Temperature Datalogger.

Is it possible or allowed to use RS-232 port with a communication protocol other than UART or it has to be always UART ?

VM111 PIC Programmer by Velleman uses RS-232 port but I am not sure if UART protocol is there or not ? If UART then it is possible to use UART to USB FTDI bridge with VM111 ?
 

betwixt

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As Klaus stated, RS232 is a voltage level definition for serial communications, it has nothing to do with UARTs although in most cases one is 'behind' the RS232 interface. A UART is a serial to parallel and parallel to serial converter with extra framing circuits and error detection circuits, it can be used for any kind of serial data.

A protocol defines a method of passing data between two devices, it refers to almost every serial interface whether it is a modem, programmer, Ethernet, GPS etc. It just describes the format of the data bits and how the receiving end should respond to them.

You can use a single RS232 port for many purposes, it depends on the software driving and listening to the port. There is no such thing as UART protocol though.

Brian.
 

dick_freebird

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"Back in the day" (like, '60s through '90s) RS-232 was
the most common PC interface (other than printer
port).

If you have no RS-232 port there are USB-serial
dongles that will do the job. Their quality varies, in
automotive tuning we found some better compatible
with the software than others but they're so cheap
you could buy a couple of the recognized brands
and find one that works. The logging software
ought to find the port, or a short list of them for you.

Now if you wanted to "roll your own" (poll your own)
then it might need some digging to find the format
info to code up the "handler".
 

joniengr

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Two more questions regarding RS-232 port and UART protocol.

1- VM111 PIC Programmer by Velleman uses RS-232 port to connect programming cable to PC. Is is possible to use UART to USB FTDI bridge with VM111 if PC does not have RS-232 Com port available ?
2- Is it possible to implement any other Baud rate other then the standard Baud rates which are 1200, 4800, 9600 etc ? How about using 10000 in Microcontroller and also in PuTTy terminal ?
 

FvM

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The first question has been already answered in general. If it specifically work with the said programmer has to be evaluated, or answered by the vendor. I guess yes.

As for the second question, the linked AN may help you. https://www.ftdichip.com/Support/Documents/AppNotes/AN232B-05_BaudRates.pdf

Non standard baud rates need to be defined in the driver configuration.
 

joniengr

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Another question related to UART and RS-232. If I use MCP 2221 which is UART to USB bridge with Microcontroller. Then I need to connect Tx, Rx of the Microcontroller to MCP with common ground. Is it possible to include or implement CRC in this manner with MCP bridge ?
 

KlausST

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Hi,

CRC has nothing to to with
* the voltage levels
* UART
* USB
* RS232
...

It is part of a protocol. This means: the data you send and how you interpret them.

I really recommend to do in internet search...

Klaus
 

FvM

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MCP2221 is a hardware USB CDC/HID bridge, it doesn't involve a microcontroller core. As for the UART functionality, it's similar to popular USB-to-UART bridges from FTDI, SiliconLabs or Prolific.

What do you mean with implementing CRC?
 

FvM

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The emphasis is on implementing, not the meaning of CRC. How should it be implemented in the bridge device which is just transporting UART characters?

If you build an intelligent USB to UART converter, e.g. in a PIC processor, it could implement a protocol translation and may be add or strip CRC. But as stated, MCP 2221 has no intelligent features.
 

joniengr

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I understand that MCP2221 is just a UART character transfer device which bridge or map UART to USB. The CRC is a part of protocol and can be implemented on transmitter and receiver, and the CRC has to be transported through tx ad rx pins.
 

FvM

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O.k., if your protocol includes CRC, it will be transported through MCP bridge like any other data. So what are you specifically asking about CRC and MCP2221?
 

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