Serial Ports
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- Опубликовано: 7 июл 2024
- In this video from ITFreeTraining, I will look at serial ports. Serial ports have been around since the first personal computers, but are largely obsolete nowadays. If you are fixing or working with some old equipment you may still come across them.
Download the PDF handout: itfreetraining.com/handouts/ap...
Serial Ports
0:16 A serial interface is an interface that transfers data one bit at a time. In the early days of computing, pretty much every computer came with one or two serial ports - generally, one small and one large one.
There are many devices in a computer that use serial communication. A good example of this is the Universal Serial Bus or USB. There is, however, only one type of connection that is referred to as a serial port. Serial ports, like the one shown, use what is referred to as the RS-232 standard. This standard defines how data is sent over the port. For this reason, you may hear a serial connection referred to as an RS-232 connection. They are also commonly referred to as communication ports or com ports for short.
The serial ports themselves are called DE-9 and DB-25. The D refers to the shape of the connector. The letters E and B refers to the size of the connector. The number at the end refers to the number of pins in the connection.
To fully meet the RS-232 standard, the serial port required 25 pins. Both connectors shown use serial communication. Since serial communication is used, this essentially means that only two pins are required for data transfer - one to transmit data and one to receive data. Thus, both connectors have the same number of pins used for data. What is different, however, is the larger connector has more pins that are used for signaling.
Even back when serial ports were being used, there were very few devices on the market that required the extra pins for signaling. For this reason, generally as time passed, only the smaller serial ports were used. To implement the larger serial port cost more money and, if the functionality was not being used, it was a waste of time.
As time passed, some computers would have two smaller serial ports. Later still, the serial ports on computers started to decline, so only one of the smaller serial ports was included. Nowadays, you won’t find a serial port on a computer. Some motherboards will have a header where a serial port can be added, otherwise they won’t have anything. As time goes on, it is expected that the serial port will disappear from the computer all together.
Nowadays, generally the only time you will use a serial port is when working with old equipment or accessing certain hardware devices. Let’s have a look at how you may go about doing this.
Serial Port Access
2:50 If your motherboard has a serial port header, you can purchase a bracket with a cable that will plug into the header on the motherboard. It is just a matter of installing the bracket in a free expansion slot on the motherboard.
You can also purchase a USB to serial port cable. This is the easy option nowadays. Given that the administrator will rarely need access to a serial port, the USB cable is something the administrator can keep around for when they need it. Often a technician will use a serial port to access equipment. This will often be done just out of convenience using a laptop. A bracket cannot be installed in a laptop so the USB to serial cable is a good option.
In some cases, you may need to change the serial port from one type to another. To do this, you can use an adapter. This adapter will convert DE-9 to DB-25. You can also get adapters that change the gender of the connection. Sometimes this may be useful. Nowadays, generally the USB to serial cable will work in most cases.
Now let’s have a look at how you would access a device using the serial port.
Demonstration
3:58 There are many different software programs that can be used to access the serial port. In this demonstration I will use some free software called Putty. Putty can always be used for secure shell, telnet and serial connections. It has a lot of features and is free, so it is good software for the administrator to have.
Serial connections are not automatically configured like a lot of modern computer components. In most cases, a serial connection is a last resort. If you have another way of accessing the device, I would use that.
Description too long for RUclips. Please see the following link for the rest of the description. itfreetraining.com/ap/1c30
References
“The Official CompTIA A+ Core Study Guide (Exam 220-1001)” Chapter 3 Lesson 10592-10785
“CompTIA A+ Certification exam guide. Tenth edition” Pages 391-392
“Serial port” en.wikipedia.org/wiki/Serial_...
“RS-232” en.wikipedia.org/wiki/RS-232
Credits
Trainer: Austin Mason ITFreeTraining.com
Voice Talent: HP Lewis hplewis.com
Quality Assurance: Brett Batson www.pbb-proofreading.uk
Nice to see someone knows that DE-9 is the correct term for a 9 pin connector, not DB-9. I've been working with serial ports for over 50 years and at one point in my career had to order lots of connectors.
BTW, the 9 pin connector came in with the IBM AT computer. The IBM PC & XT used 25 pins. Until then I had never seen a 9 pin serial port.
Thanks. It has been a long time since I used an XT computer so I will take your word for it.
I run into "serial port" at times and didn't really know about it... I will save this very useful video... thanks a lot!!!
Glad to hear that!
Very good information! I was in IT back in the 1980s and these things still give me nightmares. Modems, printers, scanners, computer to computer.... There was the way manuals said it would work, and the way it actually worked. We made "breakout boxes" with wires from DB25 ribbon cables soldered wire by wire to breadboards. LEDs in the proper places could show us what was really happening.
It's fascinating to hear about your experiences in the IT world from back in the 1980s! The technology landscape has certainly come a long way since then, and it's always interesting to reflect on how far we've progressed. Dealing with modems, printers, scanners, and the intricacies of computer-to-computer communication back then could indeed be quite challenging.
The "breakout boxes" you mentioned, with LEDs to provide real-time insight into data flow and signal status, were ingenious solutions for troubleshooting and debugging. They highlight the creative problem-solving that was often required in those early days of computing.
Thanks for sharing.
Very well explained. Definitely you got parallel bus port called talent. Smooth and crispy 👏😃
Thanks for this! It is really informative. I am doing Google IT learning and needed further explanation! Thanks so much!
Great to hear!
Working on a pc of my own rn. Thanks! You helped me here.
Glad I could help!
Excellent, thanks.
Glad it was helpful!
U deserve million subs. Keep doing u r such a useful work .
😄😄😄😄😄😄😄😄💩
Thanks for the video!
Thanks for watching.
Two pieces of information I learned from this is serial ports are also referred to as RS-232. The other is the smaller plug configuration is called a DE-9. I thought it was called a DB-9
Is there any tutorial about the booting up between win-OS putty and serial-COM devices? ...maybe a generic one. 😯
*"...largely obsolete..."* Only for home users but if you're in a headend or a datacentre they are everywhere with the biggest challenge being getting your USB converter to talk to the equipment :-)
Pretty much obsolete nowadays, but mostly help when factory resetting a device.
i need to download some files to a usb stick from an older laptop that only has an rs232 port can and how can this be done cheers
I have some old digital cameras that needs serial cable to connect to a computer.
Thanks
Thanks for watching.
thank you
You're welcome
Thank you. I had a question ,I hope it get answered please. What if the device I'm trying to connect to is USB but the software is the old software and only communicates via serial. Is it possible to use the old software running a device that uses USB
USB and serial are different protocols. So probably not. Unless the USB connection appears in your computer as a serial port.
Thank you. One question: if I buy an adapter from DE-9 to DB-25, then 9 of 25 DB-25 pins will be used, right? So what would other free 16 pins on the DB-25 side do? Would they just sit there and do nothing?
The extra pins provide some additional control signals etc, however it was pretty rare even back in the old days for devices to use them. Thus as time when on everyone started using the smaller connector. So if you use the adapters like what you are suggesting it is unlikely to cause problems since the extra wires were rarely used.
Well, I was asking because if I can only control 9 pins, then who controls the other 16?
@@rimantasri4578 They just aren't used.
Thank you. Working on my A+, and even though I had other content to refer myself to, I found this very useful. Now I understand what a COM port is in the first place. I am still wondering why there are only 4 Communication ports? Subscribed.
On the original computers there was two com ports due to limitations with hardware. As hardware got better you can have pretty much as many com ports as you want. However, due to it being old technology, you don't see com ports used that much nowadays.
Does anyone know the pinout for a 26 pin header on an old multi I/O card in IBM PC?... They have changed to 10 pin a long time ago (connecting the controller to either DB9 or DB25), but I have a REALLY OLD one: a Microforce PLB-85, in my IBM 5150... Next to nothing about this card in the net (it's RAM + RTC + parallel + serial + game), and for serial it has a 26 IDC header (just like for parallel) - labelled "ASYNC 1".... Wouldn't want to "try and fry".
Sorry, don't know the answer to that. Most ports don't use all the pins, so you could try an adapter to use the small one if you need to. You can always try some random settings to see if you get something working. If you are getting random characters you probably need to change the parity or flow control.
I asked Chatgpt for an answer, but did not know either.
ChatGPT
The pinout for a 26-pin header on an old multi I/O card can vary depending on the specific card and manufacturer. However, there are some standard pin assignments that are commonly used.
Pin 1 is usually located at the top left-hand corner of the connector when viewed from the front, with the pins numbered from left to right and top to bottom. The pinout for a typical 26-pin header is as follows:
1. DCD (Data Carrier Detect)
2. RD (Received Data)
3. TD (Transmitted Data)
4. DTR (Data Terminal Ready)
5. GND (Signal Ground)
6. DSR (Data Set Ready)
7. RTS (Request to Send)
8. CTS (Clear to Send)
9. RI (Ring Indicator)
10. NC (No Connection)
11. NC
12. NC
13. NC
14. NC
15. NC
16. NC
17. NC
18. NC
19. NC
20. NC
21. NC
22. NC
23. NC
24. NC
25. NC
26. NC
However, since you have an old Microforce PLB-85 multi I/O card, it would be best to refer to the manual or documentation that came with the card to get the correct pinout. If you don't have access to the documentation, you may want to contact the manufacturer or a vintage computer enthusiast group for assistance.
@@itfreetraining Thanks so much for such a quick response! ChatGPT is quite amazing, but I'm afraid the only thing it got right is "can vary depending on the specific card" (I can see on the PCB that some of those pins are not connected at all...) Perhaps I should try to trace some of these pins to "obvious" legs of 8250, this might give me some clues. Anyway, thanks for trying to help. Interesting, how unknown this card seems to be - I bought it with my 5150, it is topping up RAM to the full 512kb, has RTC, parallel, gameport... The serial socket has never been there, I just decided one day "it would be nice to try some mice", hence my preocupation with putting this - so far bare - connector into use.
@@LoftBits I think you are on the right track to work out what this is.
I found this, but not able to verify the information yet.
The male DB-25 is the second-oldest serial computing port, referred to as COM2, and the standard 25-pin D-shell connector for EIA-232 serial communication. Various RS-232 communications devices use the male version. The female DB-25 is primarily used for computer printer ports.
So I wonder if that second port is a serial port for very old serial printers. Which must be very old since parallel has been used for a long time.
what's the use of male vga(the ones that's in vga wires) when they're in the motherboard?
If you CPU supports graphics, you can use it to display graphics.
@@itfreetraining what does that mean?
@@grinnazeed If your CPU support graphics and your motherboard has a VGA port, you can plug the VGA port into a monitor and use it for graphics.
@@itfreetraining I know video output, what I'm asking is what does the male VGA port in my computer works? It's called a Serial port, what does that do?
@@grinnazeed When you say male VGA port, do you mean the serial port? VGA port is for graphic and the serial port is a connector by which a device can send data one bit at a time may to the computer.
Hi! I bought a device with a software which only works with a usb key. I would like to know what that usb key sends to the PC and try to replicate it. Do you have some tip how to read it? Can the Putty help me in this situation?
You would need to get a USB sniffer to look at the traffic. If the USB key is used for copy protection then it most likely uses a challenge response system. Essentially the computer sends a challenge to the USB key, the USB key has information in it that is can generate the correct response. Thus, getting the USB traffic does not help since you don't know what secret is stored in USB key to generate the response.
2:22 I have a motherboard that has a serial port and lga 1151
Makes you wonder how long they will keep putting the serial port on the motherboard. My guess it will be phased out one day.
The fact you say that serial ports are largely obsolete is not true at all, still often used in embedded and industrial fields a LOT. Also sorry to say it but this video is not any more helpful than the first paragraph of the wikipedia page in my opinion.
I agree 💯👍
We probably should re-word that a bit better. In the IT world they are largely obsolete. However, serial is still used in electronics and some equipment.
The video is part of the A+ course. There is not much that people need to know to pass the exam when it comes to serial ports, so we don't go into a lot of detail.
Understandable @@itfreetraining