Quad UART?

Douglas Miller

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Jan 23, 2022, 9:54:33 AM1/23/22

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I just caught wind of various quad versions of the INS8250-style UART.
Two I'v seen so far are SC16C554B and OX16C954B. I'm wondering if those
have been considered as a way to get all the original Heath serial ports
on the H8? I'm finding a lot of variation in part numbering, so it's
difficult to track down exactly what stock and price would be.

They are available in PLCC68 packages, which would allow for use of a
thru-hole socket. The same socket, by the way, as used by the PLCC
version of the Z180 I expect we'd use for the H8-Z180 board. PLCC does
have at least one drawback: you cannot remove the chip from the socket
with mere mortal tools. I've worked with a PLCC32 EEPROM and found, with
the right (and not "cheap") tool and some practice, it goes pretty
smoothly. Of course, the force required for PLCC68 is quit a bit more
than PLCC32.

I suspect we could make a new daughterboard for the latest versions CPU
boards. Of course, getting 4 serial ports off the board would be quite a
trick - if we stick with the 15-pin molex connectors. We could consider
alternatives for exporting the serial port signals. And, I don't think
all 4 chip-select signals are brought out near the UART, either (the I/O
decoder does generate them, though).

This all hinges on whether there is any demand for more serial ports.
MP/M might use them, but I don't expect there to be much real demand for
MP/M (but who knows, a 4-terminal/3+printer H8 running MP/M might make a
good demo at a show).

Dave McGuire

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Jan 23, 2022, 10:01:17 AM1/23/22

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On 1/23/22 9:54 AM, Douglas Miller wrote:
> PLCC does
> have at least one drawback: you cannot remove the chip from the socket
> with mere mortal tools. I've worked with a PLCC32 EEPROM and found, with
> the right (and not "cheap") tool and some practice, it goes pretty
> smoothly. Of course, the force required for PLCC68 is quit a bit more
> than PLCC32.

Like anything else, it does require the proper tool.

However, there's no need to agonize over it. The proper tool costs a
painful six bucks on Amazon. Search for "PLCC extractor". I think I
paid fifteen bucks for mine, from Mouser, 20+ years ago while they were
still "expensive".

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

Douglas Miller

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Jan 23, 2022, 10:20:46 AM1/23/22

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Yeah, I got one of those when I started to work with PLCC32 EEPROMs in
the MinZ. At least for me, I couldn't make it work right on PLCC32, and
decided I had zero chance of safely extracting a PLCC68 with it. I then
got this one:
https://hakkousa.com/products/chp-tools/chp-plcc-32-extractor-tool.html
and was able to reliably extract (still took a little practice). This
tool, though, is customized for a particular pin count. I got the PLCC32
version, which can't be used on PLCC68.

On 1/23/22 9:01 AM, Dave McGuire wrote:

...The proper tool costs a painful six bucks on Amazon. Search for
"PLCC extractor"....

Dave McGuire

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Jan 23, 2022, 10:24:23 AM1/23/22

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The "scissor type" plastic ones do require slightly different
techniques for the different sizes of PLCC package, but with care, they
will work fine.

For the smaller packages, less than 44 pins, try to keep the tool as
close to vertical as possible, and get the hooks down into the slots as
far as possible before squeezing the tool. With a little practice, this
works fine. I use that tool on PLCCs of all sizes with great success.

-Dave

Douglas Miller

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Jan 23, 2022, 11:23:01 AM1/23/22

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Either way, it's probably unlikely most users would need to pull the
UART, or CPU. Certainly not the way I was doing when developing ROM
software. My original point was, unlike DIPs, you've got (little to) no
chance of safely extracting a PLCC using something like a tony screw
driver, or other "handy" bench tool.

Dave McGuire

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Jan 23, 2022, 12:04:20 PM1/23/22

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Agreed on all points. But I want to point out that we're not talking about some new-fangled exotic thing that nobody has ever heard of, or the exclusive domain of megacorps with unlimited budgets. These are very pedestrian IC packages that have been common for forty years, that can be manipulated with tools that are cheap and available to even the most timid and frugal hobbyist.

-Dave

On January 23, 2022 11:23:11 AM Douglas Miller <durga...@gmail.com> wrote:>Either way, it's probably unlikely most users would need to pull the

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Douglas Miller

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Jan 23, 2022, 12:56:56 PM1/23/22

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Yes, my point as well. We don't have to be limited to DIP packaging.

Glenn Roberts

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Jan 23, 2022, 4:01:12 PM1/23/22

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The idea of a quad serial port on the CPU board is cool. Back In The Day I don’t think I ever used more than three (console, printer, modem) and so far I’ve been fine with two ports on the existing boards, but if there are no technical complications I support the quad UART idea for future boards. Would be nice if it meant eliminating the piggyback serial daughterboard.

Sent from my iPad

> On Jan 23, 2022, at 12:56 PM, Douglas Miller <durga...@gmail.com> wrote:
>
> Yes, my point as well. We don't have to be limited to DIP packaging.

> To view this discussion on the web visit https://groups.google.com/d/msgid/sebhc/9a97cee6-c82b-e803-ca59-cf6b08a623d5%40gmail.com.

norberto...@koyado.com

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Jan 23, 2022, 11:10:52 PM1/23/22

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It has to be HW/SW compatible with the 16C550 UART. The only way to tell is for someone to buy the IC + PLCC-68 to dip adapter to test out on the Z80 V4 board. If this works, then we can add to the Z80 V5 board.

For removing PLCC IC’s from the sockets, I learned back at DEC to use a very, very small screwdriver to lift one side first and then the second slowly to avoid putting a lot of force into the socket. I never had any issues with this technique. The extractor tool never worked for me.

Proto Advantage - PLCC-68 Socket to PGA-68 Adapter (1.27 mm pitch, 25 x 25 mm body