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42

Five-bit teletypewriter codes ("Baudot", etc.) As far back as the early 1900s (believe it or not) there were teletypewriters. They were intended to replace Morse-style telegraphy, directly printing hardcopy rather than requiring an operator to listen to the Morse code and transcribe the messages by hand. The first successful such equipment was invented by ...


26

It's not dark magic, it's just that there is no hardware limit for 9600 bps to begin with. There are many factors at play here, it's just not about the UART chip. The speed depends on basically from these items: Design & marketing plans/specs of an IBM PC before hardware was designed CPU speed ISA bus speed between CPU and UART Disk transfer speed The ...


22

Simply, a UART is a serial port, but a serial port is not neccessary a UART. Serial port is a general term for anything serial, without further specification, while a UART defines a tranceiver for a specific asynchronus format. That Ports using asynchronus protocols like RS232 ot TTY are colloquially simplified as serial port shouldn't promote technical ...


22

A tight polling loop can easily achieve a solid transfer speed of 11,520 bytes/second over a 115,200 baud serial link, even when using a moderately slow processor. Even if a processor can only run 250,000 instructions/second (which is pretty slow), it could afford to spend more than 20 instructions dealing with each byte. Disabling interrupts would likely ...


21

Prepare hardware Gather hardware Get or make a serial cable from HP48 to DB9 (most common) or DB25 (instructions on https://www.hpcalc.org/hp48/docs/faq/48faq-12.html, the core of it being: looking at the calculator socket from left to right, pins are shield,tx,rx,ground ). Get a USB-to-Serial adapter with matching DB connector, or add an adapter. Beware, ...


19

The pre-ADB Macintoshes use a simple quadrature-encoded mouse input, no formal serial protocol. Quadrature encoding is a simple, physical process, that lends itself to a convenient cheat if you're synthesising input. Picture a cog, with an optical sensor pointing through the grooves. If you observed the digital output of that sensor, you'd be able to tell ...


17

The C64 does not have a real standard RS-232 port. (The C64 port marked Serial is something quite different, namely its native IEC port.) The User Port, however - apart from being usable as a a parallel port - can almost be used as an RS-232 port as well. The "OS" (kernal) has support for it, but the voltage levels are +5/0 instead of the ±12V of ...


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 Baudot code uses 5 bits, and IIRC at least one of the mechanical teleprinters needed 1.5 stop bits to provide the time for the mechanism to do its thing, this at 45 baud. RTTY radio comms is probably the one place you still see this stuff in use. 9 bit on the other hand is semi common in RS485 industrial controllers.


15

This is the Winchester connector. The form factor is specified in ISO 2593. ISO standards are typically not available for free, which may be why you had trouble finding information on it. I'm not aware of any standard actually specifying it for v.35. The first link above (to the O'Reilly book) suggests it was simply a de facto industry standard. This ...


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

Traditional Teletypes and many paper tape storage systems use these. You won't be able to read reels of punched paper tape if you drop support for 5 bit data. Nor will you be able to interface with Colossus systems, or the Lorentz communications they were designed to decode. At least one of each is apparently still in service - as a museum piece. Full ...


13

The BIOS list only contains addresses of up to four standard 8250-type COM ports found at boot at the standard addresses. It will not contain more than four ports, it will not contain any non-8250 type COM ports, and COM ports at non-standard addresses, such as PCIE COM ports, and USB COM ports which don't have an IO address to begin with. It will not ...


13

Well, this is to be expected; the BIOS Data Area has only four slots for I/O addresses of serial ports, with slots for parallel ports immediately following. In the MEMORY.LST file from Ralf Brown’s, we can find the following entries0: MEM 0040h:0000h - BASE I/O ADDRESS OF FIRST SERIAL I/O PORT MEM 0040h:0002h - BASE I/O ADDRESS OF SECOND SERIAL I/O PORT ...


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 ...


12

Just one example: The Trimble GPS receiver's (used on agricultural positioning systems, for example) proprietary TSIP protocol (roughly end of the century, so somewhat retro already) uses odd parity by default. Odd parity has one marginal advantage over even, at least for even bit-lengths: If you have the data input stuck at 0 or 1 (which is a probably more ...


11

Some sort of comms program that supports Zmodem on the 286 end and use "sz" to send from the unix end. Zmodem has some advantages in that usually the receiving computer will auto start reception of a file when it sees a Zmodem start sequence (there's a random number handshake to stop spoofing) The reason for recommending Zmodem is means you don't need to ...


11

I successfully got the RK-P400C printing from a serial console (minicom on Linux) today. Here's how to do it for future reference...;) The DB25 connector on the right side is a 25 pin serial port. At the top right of the typewriter there are sets of switches to select font and size, at the far right of those are two switches with the labels "KBI, KBII, EXT" ...


11

I posted a comment on the reverse-engineering Q&A you linked before I realized it'd do better as an answer here. The answerer there found that googling Accom and Axial from your photo turns up a series of video editing controllers, and documentation for a DE-9 connector. If it's an editing controller running RS-422 over DE-9, it's almost certainly Sony 9-...


10

You can also use dosbox or dosemu to run a simulated DOS environment, give it access to whatever ttyS* or ttyUSB* you have, and then use the DOS-to-DOS transfer methods. Personally, I prefer Laplink, which offers a convenient Norton-Commander like interface for file transfer. It can also bootstrap via the CTTY command on the remote computer, which is handy ...


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

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'...


9

By the time I got my first analog modem, around 1980, my experience was the same as yours. Even and odd parity on 7-bit data was available, but almost all the BBSs featured 8N1. (The modems even still supported 5- and 6-bit data streams.) Apparently noise on phone lines by that time was so low that parity detection was considered superfluous for a large ...


9

It would be useful to establish whether anyone knows of any application for these which is still in service. RTTY (FSK modem over radio) still uses 5 bit code at low bitrates 45/50. It's often still used for automatic weather reports. What were the legacy applications for 5 or 6 bit serial data, and do any of them still exist? The six bit code was ...


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 ...


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

Parity is a "one-bit checksum over a single character". It can be used to detect single-bit errors in a serial asynchronous link (As the checksum is only one bit, two or more bits/char failed transmission can go undetected). Parity "even" adds a bit so that the sum of all data bits in the byte frame is even, while "odd" parity does the same so that the sum ...


7

This has already been well answered, but I wanted to respond with a couple of bootstrap solutions: that is, if all you have is a Linux box connected to a DOS box via a null-modem cable. minicom on Linux includes the ascii-xfr program. It's used as the default text file transfer protocol. By using its [-l linedelay] and [-c characterdelay] options it can be ...


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