manual programmable uart

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I'm looking for a very simple uart I can use that will allow setting baud config manually (like with dip switches or pull ups).  Would like to read the uart data via pins (Shift Register of characters/data) . Looking for a no program logic solution. Anything like that out there?

 

Last Edited: Wed. Nov 14, 2018 - 12:57 PM
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Can't you just employ a small/cheap MCU ?

 

If you were to get just a standalone UART (like the venerable old 8251) you'd end up needing a micro to control it anyway. So why not pick a micro that already has a UART in it?

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Na, special project in this case. I have many micros that can do this. Not a task, just an experiment. I figure something had to be available in the early 80s that did this.

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Yeah, a lot of the original 8080 and Z80 and later 808/8086 machines all employed the 8251 then later the 16550 which is like a "grown up" 8251 with buffering and stuff.

 

Perhaps the most famous user of the 8251 was the IBM PC and because of that it became something of a "standard"

 

Wonder if ebay has old relics like "ISA UART card" - that would have the chip mounted.

 

EDIT: Ok so very few hits for 8251 based ISA UART cards - but there seem to be loads of 16550 based ones like:

 

https://www.ebay.co.uk/p/2-Port-...

 

You can see two 40 pin DIPs on that - they are 16550s

 

(Blimey, if I'd know that $5 UART cards would sell for £30..£50 about 30 years later I would have bought a box full!)

Last Edited: Wed. Nov 14, 2018 - 01:09 PM
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The really simple early UARTs were things like the 6402. But they ran with external x16 clock inputs.

 

 

[E2A]

Looks like you want one of those and a 4702/4712 baud rate generator.

 

 

[E2A]

Both available on eBay. Plus the MC14411 baud rate generator.

#1 This forum helps those that help themselves

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#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

Last Edited: Wed. Nov 14, 2018 - 01:39 PM
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IIRC, the early serial interface chips required an external baud rate clock, usually at 16x the baud rate, and it was common to have dip switches to chose which clock you needed.

 

Jim

 

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Cliff, the 8251 and 8250 were very different beasts. The 8251 was Intel, the 8250 was Western Digital methinks.

As for why you’d use a real UART these days is beyond me - a micro and a crystal can be programmed to do the same thing better.

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S_K_U_N_X wrote:

I'm looking for a very simple uart I can use that will allow setting baud config manually (like with dip switches or pull ups).  Would like to read the uart data via pins (Shift Register of characters/data) . Looking for a no program logic solution. Anything like that out there?

 

You need to go back a very long way to find a UART without internal registers.  IIRC there was a (Motorola? **) DIP40 CMOS UART-remote IO part that had device Address pins and IO pins, not sure what baud choices there were.

Here in 2018, almost any 25c MCU could  allow setting baud config manually (like with dip switches or pull ups) & read the uart data via pins

 

 

addit:

 Found it :  MC14469 Addressable Asynchronous Receiver/Transmitter  - can even be found on eBay for eye watering price. ( more than a Raspberry Pi Zero... )

Last Edited: Thu. Nov 15, 2018 - 12:40 AM
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The 6402 is probably what you want.   External clock, though.   You'll definitely end up with a circuit more complex than a 40pin micro with switches attached.

 

I last used a couple in ~1981, to make a 75bps to 300bps converter that allowed a newswire to stream into our mainframe, so that the results could be searched/etc.

That used a 555 for the clock, a couple flipflops to get the slower clock, and two of the UARTs, and maybe a gate or two  No smarts required.  (Since I had a "known" continuous data source, I stuck a LED on the "Framing Error" output, and adjusted a pot on the 555 till it stopped flashing.)

 

Bought them from JameCo, and they still have some: HD6402 UART at JameCo

I guess the other popular part was the AY-5-1O13 /4/5  (PMOS (w -12V required), CMOS 5-14V, and CMOS 5V, respectively)

 

It's a little bit shocking how few of these "dumb" UART chips were available before the advent of internal-register microprocess-oriented chips came along.

 

It's also relatively easy to build yourself a UART out of logic chips.   There were articles in the hobby magazines in the early days with circuits...

 

 

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How many combinations do you need?

 

A  tone generator can make some different legal bytes if it's just 8n1 , and if the duty cycle are different from 50% there are 8 legal bytes.(FF FE FC F8 F0 E0 C0 80 00)

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RCA made a  cmos uart that did not need a cpu to control it. I built a serial to parallel converter in about 1980 with one. It may have been a CDP1854 or CPD6402. I still have it, but it's buried deep. It could t/r over 200 Kbaud.

 

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The largest hospital in the Southern hemisphere at that time (Westmead hospital in Sydney about 40 years ago) ran the nurse call system on such a scheme with a clocked UART (Motorola??) and lots of parallel in/serial out and serial in/parallel out chips, very good for that time but easily replaceable nowadays with a small micro and a few latches if the micro did not have enough inputs.

 

One of my jobs at the company I use to work for was to test the WECs (Ward Equipment Cabinet) by looking at the ASCII codes coming out of the UART on a screen, a job where you end up cross eyed! From memory it was just all printable chars with upper case only.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I have made exactly what was requested with a Tiny2313. There was an external crystal clock available so I did not need to add a clock. Of course, the 2313 needed programming but the distributor, at the time (Arrow, maybe) had automated programming capability.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

Last Edited: Thu. Nov 15, 2018 - 01:18 AM
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westfw wrote:
It's also relatively easy to build yourself a UART out of logic chips.
Likewise with cPLD or FPGA and their schematic-like tools; 5V cPLD are an order of magnitude less expensive than 5V FPGA.

GitHub has a plethora of UART in HDL; much less so at OpenCores.

An FPGA's design catalog is also much less though easier to search.

 

https://opencores.org/projects?expanded=Communication%20controller

D16450: Configurable UART - Lattice Semiconductor

...

The separate BAUD CLK line allows to set an exact transmission speed, while the UART internal logic is clocked with the CPU frequency.

...

 

"Dare to be naïve." - Buckminster Fuller

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I think I still have a bunch of 16550 and 851 s in a storage box somewhere.

Kept them for if I had time I could just have a nifty little play with them. hook them to a mega128 or 2560 and see if I can get things to work. Just for fun and learning.