40
votes
Why was RS-232 12V?
There are maybe a few points left out here.
RS-232 was first recommended in 1960.
That's long before there were low-voltage devices. In fact, it was originally designed to work with electro-...
- 213k
31
votes
Accepted
What is the serial protocol commonly used over RS-232 (among other links) and where did it come from?
The bit-serial protocol that is most often used to transfer data frames over RS-232 interface is simply called the "asynchronous start-stop protocol", a method that was patented already in ...
- 28.3k
30
votes
Did terminals (e.g. VT100) require a terminal driver on the host computer?
Different terminals didn’t (and don’t) use different kernel-level drivers. In Unix-style systems, the kernel does provide some terminal-related features, called line disciplines and the TTY layer ...
- 118k
25
votes
Why did Linux standardise on RTS/CTS flow control for serial ports
In short, Linux is a Unix-like operating system kernel and does things like other Unix-like operating systems. The least common denominator for different Unix-like systems is the POSIX standard, which,...
- 28.3k
21
votes
Accepted
Advantage of RS-232 over 20mA current loop
TL;DR:
It's a classic case of technological advancement vs. installed base
In the early days of electricity-based communication (i.e., telegraph and later TTY) there was no way to detect a voltage and,...
- 213k
18
votes
Accepted
9-pin vs 10-pin serial port ribbon cables
In more recent designs, since the mid-2000s I think, it became common to include "key" pins like this to reduce assembly errors. In most cases the pin removed was non-essential in the first ...
- 16.7k
16
votes
Advantage of RS-232 over 20mA current loop
The current loop goes all the way back to classic telegraphy. If there's current flowing, then that's one state. If there's no current, then that's another state. It's as simple as it can be. You ...
- 13.5k
16
votes
Accepted
How can I connect a Psion Series 5 PDA to a 64-bit Windows PC?
Hardware
It is possible to connect the RS232 serial cable with a current Windows PC using a compatible RS232-USB adapter. I have a 'Belkin PDA Adaptor', which works well and has 64-bit drivers for ...
- 3,247
14
votes
Accepted
Early programmable calculators with RS-232
In the early seventies, companies like HP and Wang sold 'programmable desktop calculators' that were really personal computers
Not really, as they stood firmly on the calculator side. If at all, ...
- 213k
14
votes
What is the serial protocol commonly used over RS-232 (among other links) and where did it come from?
The framing protocol of 'start bit, data bits, stop bits' predates RS-232 and other voltage-based physical encodings. It was used, for example, on 20 mA current loop Teletype interfaces.
It is ...
- 33.5k
13
votes
Creating a 'bridge' between a serial port and a Telnet session in Windows 98?
In DOS, I remember being able to start COMMAND.COM on a COM port simply by doing this:
REM Set COM1 speed and settings
MODE COM1:38400,N,8,1
REM Hand over control to COM1!
COMMAND COM1
REM The ...
- 1,337
13
votes
Accepted
How do serial (user port) adapters achieve speeds above 1200bps in C64?
The RS232 routines in the ROM of the C64 use port B of the CIA (PB0-PB7 on the userport) to input/output all RS232 signals including Tx and Rx. So these routines don't actually use the shift register ...
- 26k
13
votes
Accepted
DOS serial printer formats
This question is a near duplicate of 'How can I convert Epson escape codes to a more usable format?', which lists some suggestions for tools for managing Epson sequences, but I'll provide some more ...
- 11.8k
13
votes
Why did Linux standardise on RTS/CTS flow control for serial ports
Linux started as a hobbyist operating system. It was in no position to set any kind of standard. Instead, Linux implemented what hobbyists needed at that time. When Linux got popular, the convention ...
- 7,636
12
votes
Serial Receipt Printer Garbage
Looks like inverse polarity.
The CR code is 015, 00001101 in binary.
The codes for "=" and "y" are 075 and 171, 00111101 and 01111001 respectively. Note the sequence of four zeros in CR, and ...
- 18.3k
12
votes
Accepted
DECNet physical connector
DECnet is more of a protocol suite than a physical hardware standard. So asking what kind of physical connector it uses is kind of like asking what kind of physical connector TCP/IP uses -- the ...
- 11.4k
11
votes
Accepted
How can I send RS-232 serial data to a Tandy plotter reliably?
The manual says nothing more than it can print 12 characters per second and it uses BUSY pin.
Even if you have connected BUSY output to CTS input, and turned RTS/CTS handshaking on, there is still a ...
- 28.3k
11
votes
Why was RS-232 12V?
The question is posed with the assumption that RS-232 was always ±12V.
Unfortunately, the short answer is, it was not always ±12V.
The specification requires that an RS-232 driver outputs a minimum of ...
- 28.3k
10
votes
Accepted
RS232 Tape Recorder Emulator?
I think your best bet is an RS232-USB interface (NB I'm nor recommending the particular one linked, it was just the first one that came up in my search). Plug it in to your R-Pi's USB port and it ...
- 11.4k
10
votes
Did terminals (e.g. VT100) require a terminal driver on the host computer?
This was not done by a “driver” at the OS level as you are thinking of it.
In Unix, there were drivers that dealt with the RS232 interface and these were surfaced as /dev/tty* devices and dealt with ...
- 3,264
10
votes
Did terminals (e.g. VT100) require a terminal driver on the host computer?
"It depends".
I'm answering this in the context of DEC timesharing systems, since that's the natural habitat of a DEC VT100.
There's a hardware device such as a DZ11 terminal multiplexer (8 lines) ...
- 33.5k
10
votes
Early programmable calculators with RS-232
The de facto – and indeed de jure – standard interface for computers controlling random equipment was RS-232.
Some would argue with that, at least in certain industries — Hewlett-Packard’s HPIB (GPIB,...
- 118k
10
votes
9-pin vs 10-pin serial port ribbon cables
In addition to the fact that some serial-port adapter cables have a blocked off pin, I've seen boards and cards use two different pinouts. On a DB-9 male, the pins are numbered
1 2 3 4 5
6 ...
- 34.7k
10
votes
DOS serial printer formats
This is a classic data conversion problem. I have done similar things many times over the years with both parallel and serial printer ports and a variety of different operating systems. The other ...
10
votes
Why did Linux standardise on RTS/CTS flow control for serial ports
Serial port standards weren't. Obligatory XKCD.
Different devices had different preferred handshaking lines. And even if all DCE worked the same and all DTE worked the same, you had situations of DTE -...
9
votes
Accepted
Cartridge modems - was the Vic-20 a special case?
I thought the RS-232 port on the Vic-20 was completely separate from the cartridge port, so a thing had to be plugged into one or the other, and if the modem was plugged into the latter then it could ...
- 213k
9
votes
9-pin port for both RS-232 and Atari joystick?
In the early eighties, use of a 9-pin port for serial communications was uncommon. Most systems used the standard 25-pin port. I think it was IBM that made the 9-pin serial port popular, but I don't ...
- 11.4k
9
votes
Accepted
How to connect an HX-20 to a monitor via the RS232 port?
It sounds like it can be done 'directly'
No, it can not. The interface hardware is not able to generate a valid TV signal.
The RS232C port is a true RS232C operating as positive and negative voltage....
- 213k
9
votes
Advantage of RS-232 over 20mA current loop
The advantage of RS-232 was that it was a formal standard that defined the electrical interface between equipment, down to handshake signal usage, voltage levels and connector pinout.
Even though ...
- 28.3k
8
votes
Accepted
Does the 25-pin IBM PS/1 serial port connector contain two serial ports?
According to the IBM PS/1 Technical Reference Manual, the pin assignment of the serial port is:
So to answer your question: no, there is neither a second port nor a secondary channel for the first ...
- 1,015
Only top scored, non community-wiki answers of a minimum length are eligible