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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 ...


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 ...


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 ...


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

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, ...


5

Current loops are better for signal integrity for long runs because they are generally only "grounded" to a fixed potential at the current source. This means that there's no "ground loop" for stray magnetic fields to interact with. For electromechanical devices this is easy to implement: switches and relays don't need a common "...


5

a company like DEC that made both the computers and the terminals Actually a lot of DEC computers (PDP-8, PDP-11) had teletypes as I/O devices. Teletypes used 20ma current loops so DEC needed to provide such. Only later did DECWriters and the VT series of CRTs become the usual I/O.


2

The innards of above device depicted by tofro are completely different. No PIC inside but a 74HC164 8-bit serial-in, parallel-out shift register:


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