# rs 232 help



## stuiec (Sep 25, 2010)

I have zero experience with rs232. I have an HDMI multi-viewer that has all functions but one available on the supplied ir remote. It has an rs232 3 point terminal block (Tx / Gnd / Rx). I do have a chase to the desired point of control, and the software for the HDMI box. My question is regarding the cable. 

Can I use cat6 and then an RJ45 to connect to the remote laptop 20' away?

If the laptop doesn't have and RJ45 port, can I use an RJ45-USB dongle?

Does this need to be a cross-over cable?

Am I completely out to lunch?


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## gnuuser (Jan 13, 2013)

dont know if it will help but heres a link to rs232 pinout cofigurations.
https://www.google.com/search?q=rj4...CAYQBg&biw=1366&bih=618#imgrc=E49LoB9nHI1axM:


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## sparkiez (Aug 1, 2015)

First: Ethernet is NOT RS232. They are completely different electrical standards. You need something like this: 

http://www.winford.com/products/brk...jbgZ-7W8dV9tV9ZHb-7o_Tca5kzvgiv8aAsnvEALw_wcB

And a usb to serial cable. Make sure the chipset is FTDI. They are WAAAAAAAY better than a prolific chipset. I can't understate this.

Connect the GND on your device to pin 5 of the breakout board. The TX pin to pin 2 of the breakout board and the RX pin to pin 3 of the breakout board. Then you are golden. For just 20' you can use cat6 cable, but you may need to lower the data transmit speed.


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## splatz (May 23, 2015)

If you use Cat 6 and plugs, you'll normally need RJ45 to modular adapters to plug into the serial equipment. If your PC doesn't have a serial port (rare on today's laptops, but still on most business desktops) you'll have to use a USB to serial adapter. 

Some serial equipment, like Cisco network equipment for example, instead of an old fashioned 9-pin serial port (or an even older fashioned 25-pin serial port) have an RJ45 type port for the serial console. For those, you'll want to buy or make an RJ45 to serial adapter using the manufacturer's pinout. 

If you're making up the RJ45 to modular adapters, you could use whatever you want for the pinout; for example you could use blue for RX, orange for TX, and green to signal ground. 

Technically, if the device at one end is a DTE device and the device at the other end is a DCE device, you'd use a straight through cable, same pinout at both ends. If both devices are DCE or both are DTE, you need a null modem cable, but with just three conductors that just means swap transmit and receive. Most likely you will just use a straight through cable. 

Of course if the device has screw terminals rather than an actual port you can just hardwire the three conductors to the device, and use the RJ45 to modular adapter into the serial port on the computer. 

RJ45 to serial adapter: 










USOC pinout used on RJ45 to serial adapters: 










9-pin serial pinout: 












stuiec said:


> I have zero experience with rs232. I have an HDMI multi-viewer that has all functions but one available on the supplied ir remote. It has an rs232 3 point terminal block (Tx / Gnd / Rx). I do have a chase to the desired point of control, and the software for the HDMI box. My question is regarding the cable.
> 
> Can I use cat6 and then an RJ45 to connect to the remote laptop 20' away?
> 
> ...


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## stuiec (Sep 25, 2010)

gnuuser said:


> dont know if it will help but heres a link to rs232 pinout cofigurations.
> https://www.google.com/search?q=rj4...CAYQBg&biw=1366&bih=618#imgrc=E49LoB9nHI1axM:


Thanks, and for anyone else wondering, I found this resource, seems pretty comprehensive: https://www.arcelect.com/rs232.htm


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## stuiec (Sep 25, 2010)

sparkiez said:


> First: Ethernet is NOT RS232. They are completely different electrical standards. You need something like this:
> 
> http://www.winford.com/products/brk...jbgZ-7W8dV9tV9ZHb-7o_Tca5kzvgiv8aAsnvEALw_wcB
> 
> ...


Thank you, and thanks for the heads up on the Prolific----its the first that came up on my search.


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## stuiec (Sep 25, 2010)

Parts ordered, thanks fellas!


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## sparkiez (Aug 1, 2015)

stuiec said:


> Thanks, and for anyone else wondering, I found this resource, seems pretty comprehensive: https://www.arcelect.com/rs232.htm


Thanks for following up and reminding me about this. This is actually one of the sites I used to learn about serial comms. We had all kinds of devices with crazy serial connections where I used to work, so I got pretty good at making cables and reverse engineering them. I'll have to book mark it this time.


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