24 Apr
2009
24 Apr
'09
9:56 p.m.
I purchased an 820-II from eBay, but the seller did a horrible packing job
and it arrived with the case completely smashed.
Incredibly enough, the CRT was not shattered and once I diassembled it and
spread things out, it nominally fires up. I get the monitor sign-on and a
beep, but no keyboard response at all.
I've already tried reseating everything on the system board and fixed a
bad solder joint on the crystal for the keyboard MPU. No luck.
I have some schematics from the web, but they are extremely fuzzy and hard
to read. Can anyone help with theory of operation for an 820 keyboard?
I gather that it's a parallel data interface, but past that I'm a bit in
the dark.
I should mention that I'm running without a disk drive. The seller "lost"
it and I have the carcass of another on the way from a kind cctech group
member. Still, I would think there'd be some response to keyboard input
without the drive on line.
Steve
--
25 Apr
25 Apr
9:44 p.m.
On 24 Apr 2009 at 17:56, Steven Hirsch wrote:
I have some schematics from the web, but they are
extremely fuzzy and
hard to read. Can anyone help with theory of operation for an 820
keyboard? I gather that it's a parallel data interface, but past that
I'm a bit in the dark.
The 820 series is strongly related to the Jim Ferguson "Big Board"
kits sold in the early 80's. Bitsavers has both the schematics for
the 820 and the Big Boards.
The keyboard interface is as simple as it gets--8 bit postive logic
ASCII character code and a negative-going strobe to reflect a
keypress. ISTR that BIg Board users tended to use George Risk
keyboards, but just about every keyboard maker had a parallel ASCII
model (e.g. Cherry, Keytronics, etc.). Other than looking for bad
connections or discrete components on your keyboard, there's not much
to be done, as all of the "smarts" are usually located in a single
mask-programmed keyboard interface chip.
To see if your 820 mainboard is at fault, try driving the keyboard
lines with the output of a PC's parallel port (not possible with a
"real" computer like a Mac).
--Chuck
9:52 p.m.
On Apr 25, 2009, at 5:44 PM, Chuck Guzis wrote:
...but possible in short spurts between crashes and viruses on a
PC. ;)
[sorry, I couldn't resist!]
--
Dave McGuire
Port Charlotte, FL
I have some
schematics from the web, but they are extremely fuzzy and
hard to read. Can anyone help with theory of operation for an 820
keyboard? I gather that it's a parallel data interface, but past that
I'm a bit in the dark.
The 820 series is strongly related to the Jim Ferguson "Big Board"
kits sold in the early 80's. Bitsavers has both the schematics for
the 820 and the Big Boards.
The keyboard interface is as simple as it gets--8 bit postive logic
ASCII character code and a negative-going strobe to reflect a
keypress. ISTR that BIg Board users tended to use George Risk
keyboards, but just about every keyboard maker had a parallel ASCII
model (e.g. Cherry, Keytronics, etc.). Other than looking for bad
connections or discrete components on your keyboard, there's not much
to be done, as all of the "smarts" are usually located in a single
mask-programmed keyboard interface chip.
To see if your 820 mainboard is at fault, try driving the keyboard
lines with the output of a PC's parallel port (not possible with a
"real" computer like a Mac). 
26 Apr
26 Apr
4:50 p.m.
To see if your 820 mainboard is at fault, try driving
the keyboard
lines with the output of a PC's parallel port (not possible with a
"real" computer like a Mac).
But certainly possible with real computers like PDP8s, PDP11s, PERQs,
HP9000/200s, machines with HPIB or HPIL ports (+ the right interface
converter), Commodores (most had user ports IIRC), BBC micros, etc, etc, etc
Alternatively, can't you see if the existing keyboard is sending anything
using a logic probe?
-tony
5:21 p.m.
On 26 Apr 2009 at 17:50, Tony Duell wrote:
But certainly possible with real computers like PDP8s,
PDP11s, PERQs,
HP9000/200s, machines with HPIB or HPIL ports (+ the right interface
converter), Commodores (most had user ports IIRC), BBC micros, etc,
etc, etc
It was meant as a jab to an earlier pro-Mac post about how PC's
aren't "real" computers.
Alternatively, can't you see if the existing
keyboard is sending
anything using a logic probe?
Both approaches are valid, but I suggested the parallel port because
(1) it's easy to do and (2) if it's the keyboard that's gone south,
one can use the parallel port option to check out the rest of the
machine until the keyboard fault was islolated and repaired.
--Chuck
8:08 p.m.
On 26 Apr 2009 at 17:50, Tony Duell wrote:
Sure. I was just pointing out there are plenty of real computers which do
have parallel/user ports.
But certainly possible with real computers like
PDP8s, PDP11s, PERQs,
HP9000/200s, machines with HPIB or HPIL ports (+ the right interface
converter), Commodores (most had user ports IIRC), BBC micros, etc,
etc, etc
It was meant as a jab to an earlier pro-Mac post about how PC's
aren't "real" computers. Alternatively, can't you see if the existing
keyboard is sending
anything using a logic probe?
Both approaches are valid, but I suggested the parallel port because
(1) it's easy to do and (2) if it's the keyboard that's gone south, one can use the parallel port option to check out the
rest of the
machine until the keyboard fault was islolated and repaired.
True.
-tony
8:36 p.m.
On Sat, 25 Apr 2009, Chuck Guzis wrote:
On 24 Apr 2009 at 17:56, Steven Hirsch wrote:
Very good suggestion, Chuck - thanks!
Fortunately, it turns out to have been much simpler. The 820-II firmware
apparently expects the FDC controller to be present during init. To keep
things simple, I had the daughterboard unplugged.
Once I smartened up and plugged the controller in, it started responding
to the keyboard. I can only assume it resets the controller at power up
and is waiting for some sort of state change or interrupt. Without the
board present it was just waiting forever and never getting to the stage
where it would acknowledge character input from the keyboard.
Nice when things turn out this easy.
Steve
--
I have some schematics from the web, but they are
extremely fuzzy and
hard to read. Can anyone help with theory of operation for an 820
keyboard? I gather that it's a parallel data interface, but past that
I'm a bit in the dark.
The 820 series is strongly related to the Jim Ferguson "Big Board"
kits sold in the early 80's. Bitsavers has both the schematics for
the 820 and the Big Boards.
The keyboard interface is as simple as it gets--8 bit postive logic
ASCII character code and a negative-going strobe to reflect a
keypress. ISTR that BIg Board users tended to use George Risk
keyboards, but just about every keyboard maker had a parallel ASCII
model (e.g. Cherry, Keytronics, etc.). Other than looking for bad
connections or discrete components on your keyboard, there's not much
to be done, as all of the "smarts" are usually located in a single
mask-programmed keyboard interface chip.
To see if your 820 mainboard is at fault, try driving the keyboard
lines with the output of a PC's parallel port (not possible with a
"real" computer like a Mac).
27 Apr
27 Apr
6:15 p.m.
Fortunately, it turns out to have been much simpler.
The 820-II firmware
apparently expects the FDC controller to be present during init. To keep
things simple, I had the daughterboard unplugged.
Once I smartened up and plugged the controller in, it started responding
to the keyboard. I can only assume it resets the controller at power up
and is waiting for some sort of state change or interrupt. Without the
board present it was just waiting forever and never getting to the stage
where it would acknowledge character input from the keyboard.
This reminds me in a way of a problem I had with a Whitechapel MG1 (A
32016-based workstation). It flashed the error LED at power-on, reporting
a multi-bit DRAM error.
TO gcut a very long story short, after battling throuhg the memory
arbitration logic, I discovered there was actually nothing wrong. The
mainboard has 512K of RAM on it, the boot ROM needs (and tests) 1.5M.
After plugging in the 2 RAM expansion boards I'd removed 'to keep things
simple' (:-)), it worked fine. This is not documented in any of the
manuals I have.
Nice when things turn out this easy.
In my case it wasn't so simple. It took me a day to go through and check
all the logic. It's a complcated machine...
-tony
5724
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