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41

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-mechanical, not electronic devices, like TTY. RS-232 uses directed voltages. So it's not simply 0V and 12V but +12V and -12V. Quite useful to work with coils. It ...


29

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 which you mention; there is typically at least a raw line discipline (which doesn’t perform any translation), and a cooked line discipline (which provides more-or-...


19

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, when needed, amplify it. Only current flowing in a closed circuit could be detected reliably—by having it run through a coil which in turn moved a lever—and ...


17

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 place, eg. an extra ground pin or a no-connect. I think in this case it is a no-connect. In the case of COM headers, there are actually two different pinouts ...


16

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 don't need to manipulate voltages. That's the key. Just turn a literal switch on and off. It also has problems. Current losses are heavy even in short ...


13

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 remote typed "exit"... You could then use a remote terminal connected to COM1 to give DOS commands on that machine - and simply type exit to return the machine ...


13

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 capabilities of the CIA, and have to do the shifting, parity calculation and bit-banging in software. That's the reason the speed is limited to about 1200 bps. ...


13

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, systems like the Cogar 4 and Datapoint 2200 are the origin of desktop computing. Complete units with a CPU, mass storage, CRT display and a full figured typewriter ...


13

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 background and information as I understand it. The IBM ProPrinter uses the IBM Personal Printer Data Stream (PPDS) page description language, which is a character ...


12

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 sequences of four ones in "=" and "y". With the inverse polarity, the character boundaries will depend on the speed with which they are sent because the start and the ...


11

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 answer is, it uses whatever connector you need to use for the particular data link layer you're running DECnet on top of. If you are running DECnet over Ethernet, ...


10

"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) that controls terminal lines by some physical protocol, such as RS232 or 20mA current loop. The physical protocol is a matter for the hardware. But the OS needs ...


10

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 things like speed, echo, etc. As for escape sequences controlling the display of the terminal, that is not done at the “driver” level as you are thinking of it....


10

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, IEE-488) was (and is) also commonly used to connect control and/or measurement equipment. It is simpler to implement than RS-232. So some early programmable ...


10

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 possibility that one or two extra bytes are sent out on the data pin, because the serial string write happens as a single large block, and also the USB packets ...


10

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 ±5V and maximum of ±15V when connected with the specified load of one RS-232 receiver. The output is allowed to have up to ±25V when no receiver is connected. ...


10

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 7 8 9 but on the 10-pin connector the pins are numbered: 2 4 6 8 10 1 3 5 7 9 I've seen some cables which connect pin 1 to 1, 2 to 2, etc. but I'...


10

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 answer focused on actual formatting of the data, which is a real issue. I will discuss the actual transfer process: The two machines have to agree on communication ...


9

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 not use the former. What am I missing? Or better what is mixed up. The device (Serial IEC) bus is often called a serial port, but that one was driven by VIA#2 ...


9

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 should appear as a device in /dev. You should be able to then read and write to it like a file (well, you might not be able to write to it if your scale is only set ...


8

Unfortunately, Hercules plug, while being the same DE-9 plug/socket as "small" RS232, is completely electrically incompatible - other than using the same connector type, there is absolutely nothing in common between the two interfaces. You can damage the card, monitor or RS232 port/converter if you try connecting RS232 with the Hercules port. So, ...


8

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 think that happened until around the time of the IBM PC AT (the original Macintosh also had a 9-pin serial port but it was wired differently, and was ...


8

RS-232 became "standard peripheral interface" later, when most of these "peripheral devices" adopted microprocessors. In early days, parallel ports were more common because they: can read-write data from logic elements like latches and d-triggers can control state of output triggers and even relays Actually they were a window to real life for CPU's ...


8

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 devices only implemented a relevant subset of the standard, and the implementations did vary and were sometimes not directly compatible, in general, only a simple ...


7

If the printer is offering an actual RS232 port, this should be identifiable by there being an RS232 level converter IC near the connector on its logic board: Usually, there will be a DS232/MAX232 or other MAX23x series IC, or a NEC D4711/UPD4711, or a combination of any of MC1488/MC1489/SN75188/SN75189/GD75189/GD75188/GD75232... This chip inverts the ...


7

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 port. All the secondary lines are not connected.


7

This can be done with a UART such as the 6402. Here's an example that converts serial to parallel:- Schematics of a Printer Adaptor Unlike more modern UARTs the 6402 does not have any internal registers that need to be 'programmed' to set it up, so it can be used standalone - and it has separate parallel read and write ports which are easier to use in a '...


7

Yes, there were such gadgets that converted serial to parallel. The attached picture shows a Miracle Serial to parallel converter for the Sinclair QL, courtesy of 1984. The QL had no ex-factory Centronics printer interface, and solutions that blocked the expansion port for connecting a printer only were not really what customers wanted, so the Centronics ...


7

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. The HX20 uses +8/-8 Volt level (*1). Voltage is generated by a TL479 step-up/down converter and used to feed the 75188 line drivers. This Voltage is way ...


7

What was the very first device to have an RS-232 serial port The question is a bit misleading, especially when tying it to 1960. RS-232 is a standard. Standards are usually made after something has been invented and used first. Their purpose is usually to either unify a varying landscape or turning de facto usage into standard (*1). Think of bolt dimension, ...


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