[sebhc] My H8 Systems

[Dwight K. Elvey]

Hi All
 Well, I got my H8 with the Z80 running. All worked fine.
I checked out my bootstrap and image transfer program
( H89LDR ) and it works fine. I sent a copy to Steven so
hopefully he gets it post to the web soon.
 I started on bring up my other H8 with the 8080 processor.
This one had seen a lot of time stored someplace where
the humidity was a little high. Many of the chips had
the silver plated pin. This is a bad idea for chips in
the long term. Any little crack in the plating and
electrolysis erodes the pins from the inside out.
 Anyway, I spent many hours tracking down failures
in the RAMs and other chips caused by pins that looked
intact but were really broken inside. I plugged in one
of the disk controller cards and used that to run its
RAM test ( Not a really great test but it found most
all of the problems, more about that later in my story ).
Some of the failures were really tricky. I found that
it is best to move possible failing parts to the lower
order bits to save testing time. It didn't seem like
I was ever going to get things working and I was beginning
to run low on spare 4K RAMs. I spent more than 8 hours
getting these to work.
 For those that are doing this, you need to have working
RAM for both the beginning and the end of memory.
It is hard to make sure all is OK when you are trying
to test. I found that it is best to have just one
working memory card at the 040.000 location and then
leave a gap between that card and the one your testing.
I would then modify the HL and DE registers from
the ones set by starting at 030.003. It takes a little
longer but some times one has to do what one can.
This kept the monitor happy and allowed testing of
really flaky boards that wuld otherwise have hung
the monitor.
 In order to get the controller card working in the
PAM8 environment, I had to undo the modifications done
to make it work with the XCON8. This included removing
a jumper and installing a 68 ohm resistor along with
a 47 pf capacitor. Luckily, this board had both the
ROM and the two RAMs still installed. The other board I
have, that I use with my Z80 machine, doesn't have these
chips.
 The RAM test that they have could be improved. Instead
of just incrementing the value, they could have use
a rotate or a lfsr to create the values. It would
significantly reduce the amount of time to test the
RAM. A full 64K system take over 10 minutes to test.
I recommend that if you are running this test that
you watch the BC register from the panel. It needs to
make a complete cycle from 000 to 377 before it had
made a complete pass through your memory. The MSB's
take for ever to get to. This is why I recommend moving
suspect RAMs to the LSB's. This only takes a few moments.
 Another thing that the test doesn't do it that it uses
the write/read type of test. It should be expanded to
to a read/write/read. It wouldn't take much to modify
since the C register isn't being used and that can
hold the previous value.
 Well, on to getting the system up and running. I plugged
my disk drive onto the system and things were looking much
better. The only problem was that the serial input wasn't
working correctly ( this is through the H8-5 board ).
I would get the <BOOT> message fine from the booting
disk but no matter what I typed, it would not continue.
It took me a while to realize that it had to be something
between the serial chip and the RS323 connector. A little
time with the scope and I realized that the optical
isolator was a little too slow. I swapped this with
the one used for transmit ( I isn't pushed quite as much
for the transmit side and can tolerate a little less )
and finally got things working.
 It was late so I didn't get a chance to play with my
H89LDR code and the H8-5 board. In any case, I now have
two H8's up and running. Yaaaayy!!
Dwight


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