[GreenKeys] MC6800 [was: Distortion Testing of my AN/FGC-25]

Sat Jul 4 15:53:52 EDT 2015

Hi Don--

Happy 4th to you too and to others on the list that observe and happy
Saturday to those who don't :-)

I see a lot of other great responses and I think everyone has converged on
contact bounce as what you are seeing.  I'm not sure if this is causing
you actual trouble with this machine communicating with another or with
a computer?

And that sort of leads me into a discussion of these old micros and their
teletype interfaces so I hope this isn't too far off-topic for the list.
I changed the subject too so folks who are not interested can just delete
the thread.

Thanks for your 6800 version of "Shooting Stars".  That's cool and
another great piece of history for these little machines.

I have both the Motorola MEK6800-D1 and -D2 kits as well as an SWTPC 6800,
an Altair 680 and a whole bunch of other Motorola EXORBUS stuff with 6802,
6808 and the later 6809 processors.

I built the SWTPC machine not too long after I got the MEK6800D1 running,
back in '76 when I was 14. I guess I pretty quickly outgrew the -D1
due to the small amount of memory.  I wrote A LOT of code on my SWTPC
machine and hooked it up to just about anything that made sense (and a
number of things that didn't).

My dad helped a lot to get these machines but I also cut a huge frigg'n
number of yards to earn the money to buy the pieces and parts I needed
too :-)  Lucky for dad, I wasn't yet into ham radio so he didn't also
have to worry about buying radio gear.  He and I did build a lot of
Heathkit stuff together though so that was awesome.

My MEK6800D1 is populated with XC68xx family parts rather than MC68xx.
This was pre-release silicon from Motorola that somehow ended up in
the -D1 kit, and if you remember, all these devices were in black foam,
glued to a block diagram of the 6800 system, shrink wrapped over, and
on the inside cover of the 3-ring binder that came with the kit.

The -D1 and the SWTPC 6800 both use the MIKBUG ROM as their monitor.
MIKBUG was designed to communicate with a Teletype, model 33ASR to be
specific, for loading code, examing and changing memory and dumping
it back out.  The 'L' and 'P' commands were LOAD and PUNCH and they
communicated with ASCII "S-RECORDS" which were a format that Motorola
invented for this processor.  An S-RECORD contains a preamble, a memory
address, a count, that many data bytes, and a checksum on the end, all
in printable ASCII that could be punched to paper tape and then loaded
back to memory later.

MIKBUG did not communicate with the Teletype using a UART though, because
at the time the -D1 board was released, they didn't yet have the MC6850
ACIA (asynchronous communications interface adapter) ready for prime time.

MIKBUG was developed prior and instead used two bits on the MC6820 PIA
(parallel interface adapter) and bit-banged the 110 baud, 7-bit, even
parity async data to and from the TTY.  The -D1 kit has both RS232 and
20mA current loop interfaces on it-- as did many similar eval/trainer
boards of the day.   I also have a KIM-1, which was the MOSTEK eval
platform for the 6502 processor and it took a very similar approach
with monitor ROM to run a keypad and LED displays but also ability to
communicate with a TTY and bit banged it in and out with a PIA too.

The Altair 680 is interesting because their monitor (which doesn't have
a catchy "bug" name) came in two flavors.  One was intended for ASCII
comms to a TTY and it used the MC6850 ACIA as the serial interface for
that, with both RS232 and current loop interfaces on the board.  But MITS
also offered a BAUDOT version of the monitor PROM and if you installed
this version (which was on a 1702 EPROM), and changed some jumpering
on the board, then your console interface could be a 5-level teletype.
They bit-banged this interface on two bits, that were simple GPIO with
a buffer and a flip-flop and no complex device such as a 6820 PIA.

I do still mess around a little with 6800 coding.  A few months ago I
built a new memory board for the Altair 680 using some modern parts,
adding battery backup and some other features and then I messed around
with some memory diagnostic code to check it out.

These days I am pretty much a Linux only shop and so I have ported
the original Motorola "freeware" cross-assembler that came out in the
early 80s from MSDOS to Linux and made a few modifications so that it
can accept the original Motorola mneumonic and operand structure (that I
see you still use!) where the instruction and the register are seperated
by a space.  ie,

	LDA A #$2A

vs

	LDAA #$2A

I learned it the first way and still want to code it that way so I
fixed the assembler to accept either format.  The second way became
"the way" when the MC6811 came out.

In the early 90s, I built some commercial stuff using MC6811 and it was
fun to be able to play with a very familiar processor architecture and
get paid for it HI HI.

A few weeks ago, a friend was scrapping some old HP computer equipment
his dad had hoarded and sadly that stuff was pretty shot from sitting
in a damp garage.  But while going over the circuit boards, I spied a
huge number of HD63A01 and HD637A01 processors on these boards-- which
were the Hitachi second source (and variant) of the MC6800.  Sort of a
6800 core with 6811 I/O.

These boards were full of them! I mean, it was like massively parallel
8-bit world! and I really do not know what function they served in those
systems.  In any case, I have saved a huge pile of those and might build
up a little board to bring one back to life.  Turns out this Hitachi
processor was extremely popular in many Japanese amateur transceivers
from the 80s too.

The 6800 got used in a lot of places.  Was a pretty popular processor
for embedded (as we call it today) applications while the 6502, which
many of the same guys invented after they left Motorola, became popular
in the personal computing and game space since that's what was in the
Apple I and II, the Atari 2600 game station and 400/800 computers,
Commodore PETs, VICs and 64s-- but those were all toys :-)   The 6800
got the real work done.  There's one in your HAL ST8000-A if you have one!

73, Chris NØJCF

On Saturday (07/04/2015 at 09:43AM -0700), Don Sentz wrote:
> Hi Chris,
> 
> Thank you for your feedback about the glitches. I do suspect the contacts even though I attempted to clean them during the recent lubrication and checkout. However, according to the manual TM11-2246 I should get a "burnishing tool" to use on the contacts, but I am not familiar with burnishing and I don't know what would be the proper burnishing tool for these contacts. Maybe other GreenKeyers could respond and advise me what I should get and how to use it.
> 
> This is so great to meet another original MEK6800D1 owner!  I, too, got mine when they first came out in 1975. I was 22 and in school at Ga. Tech. I was enrolled in the very first microcomputer course that Ga. Tech offered. Our textbook was still in draft form. Your dad was like my dad, financing my ham radio projects starting when I was 11.
> 
> The May 1976 issue of  BYTE magazine featured an article about "Shooting Stars" puzzle game written for Intel 8008. That summer I rewrote the program for MC6800 and my version ran on my fully populated MEK6800D1. My report is posted on Scribd.com,( https://www.scribd.com/doc/266427916/Shooting-Stars-Puzzle-Game-for-MC6800 ), but I am enclosing a copy for you with this email. You can copy/paste the object code from the report, after the MIKBUG command "L".
> 
> When you have time maybe you can describe your collections. Do you have lots of software for the 6800's? Do you still write code for them? I use the SWTPC MP-E Resident Assembler, paper tape version. I figured out how to make it work with PC or Mac as the MIKBUG console terminal.
> 
> -Happy 4th & 73
> -Don
> --------------------------------------------
> On Sat, 7/4/15, Chris Elmquist <chrise at pobox.com> wrote:
> 
>  Subject: Re: [GreenKeys] Distortion Testing of my AN/FGC-25
>  To: "Don Sentz" <dr.sentz at yahoo.com>
>  Cc: "GreenKeys" <greenkeys at mailman.qth.net>
>  Date: Saturday, July 4, 2015, 8:39 AM
>  
>  Don,
>  
>  What an awesome project and fabulous that you
>  used an MEK6800D1 kit for
>  the job!  When I
>  am not collecting teletypes, I am collecting Motorola
>  6800 stuff and the place is full of them
>  here.  My first computer, when
>  I was 14,
>  was an MEK6800D1 kit that my dad got for me, just before
>  that
>  processor had yet been released! 
>  Still have it, still runs.
>  
>  I will study your data and certainly respond if
>  I have any ideas but I
>  will likely defer to
>  the TTY experts on list since I'm probably better
>  with the 6800 than the teletype :-)
>  
>  My initial impression is that
>  the width of the glitches is changing
>  a lot
>  each time one occurs and so this suggests to me contact
>  bounce
>  rather than a speed or timing
>  issue.  You mentioned in the notes that
>  you
>  had cleaned the contacts.  Have you revisted that since
>  collecting
>  this data or ??
>  
>  73,
>  Chris
>  NØJCF

-- 
Chris Elmquist