Altair 8800c build thread

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Re: Altair 8800c build thread

Postby Wayne Parham » June 10th, 2022, 5:08 pm

For power distribution, I had intended to use a pair of 4-position barrier strips, to keep the AC section away from the DC section. But I decided to go with a single 8-position strip.

The DC side is simple:

5. Black Ground
6. Blue -16v
7. Violet +16v
8. Red +8

AC is like this:

1. AC neutral
2. AC line
3. fused line
4. switched line

So the AC power line comes into 1 & 2. The (3A) fuse is connected between 2 & 3. And the power switch is connected between 3 & 4. So the AC line run to the power supplies comes from the #4 lug. AC neutral is connected to #1 and switched AC line is #4.

The DC section is just straight through - The output from each supply is connected to its respective lug on one side of the barrier strip, and then the other side is connected to wires going to the backpanel. For the 9-slotter, it goes to the PS connector. For the 18-slot backpanel, it goes through some inline fuses and then onto hard-wired soldered connections on the board.

For both the 9-slot and the 18-slot boards, I used a 10 amp fuse on the 8v line, and 1 amp fuses on the +/-16 volt lines. The 9-slot board is done with (socketed) picofuses and the 18-slotter is done with inline fuses.

Altair8800c_18slot_DC_fuses.jpg
Inline DC fuses for the 18-slotter


Altair8800c_power_suplies_installed.jpg
Power supplies installed


I have not fully wired-up either system, and I haven't mounted anything on their rear panels either. I did put the fan on the 18-slotter, just to test fit and see how it looked. But it was just finger tight and came out right after clicking the photos. I'm leaving them bare because I intend to send both rear panels to a machine shop in Tulsa to have DB-37 holes punched in them. That's how I'll connect the disk drives.

I could have just passed the ribbon cable through a DB-25 hole or out just under the cover. But that didn't appeal to me. I originally intended to modify the cabinet with a nibbler tool, but the cabinet is too nice to hack up that way. I'm sure I wouldn't have been able to cut a nice clean hole. So I decided to have the hole cut at a machine shop.

I considered buying a punch - looked on eBay for one - but they're too pricey. Even the more common DB-25 connector is pretty rare these days, and a DB-37, much more so. Punches are five hundred to a grand. Not worth it for a one-off. The machine shop will cut the hole precisely for under a hundred bucks.

Last thing I did yesterday was to install all the boards and connect a couple of drives, configured as DS0 and DS1. They both worked, so that was a nice win. It's still weird that the DS0 drive was able to read and write DS/DD diskettes. The DS1 drive won't. And after I understood Mike's comments about their biasing, I can see why. So I took the time to test both with the appropriate HD diskettes, and they were both happy. Super groovy cool!

I've only tested one pair though. I've been doing most everything on the 9-slot system this far. I haven't checked the pair of drives on the 18-slotter yet. Still have that to do. And I need to check them through the DB-37 connectors too, because using them adds some length and some physical interconnects. I'll confirm it all works before sending my panels to the machine shop. If not, I'll make adjustments.

Once I have the panels back, and am closer to buttoning it all up, I'll post photos of the fully assembled Altairs and their disk drives.

Getting closer... It's getting good now!
Wayne Parham
 
Posts: 240
Joined: March 18th, 2022, 3:01 pm

Re: Altair 8800c build thread

Postby AltairClone » June 10th, 2022, 6:07 pm

Your builds are looking really good! The fuses never hurt, but the outputs from the switching power supplies are very well self-protected.

Mike
AltairClone
Site Admin
 
Posts: 632
Joined: April 5th, 2013, 10:55 am

Re: Altair 8800c build thread

Postby Wayne Parham » June 12th, 2022, 9:53 am

Yeah, I know those supplies will crowbar and protect themselves. But I thought fuses would be cool too.

Hey - I just flipped the switch on the FDC to mode 5 and created a few 1.5Kb CP/M disks. They boot just fine. Love it!

But I was going to format a blank disk and found there was no FORMAT.COM on the 1.5Kb (CPM22-48K-HDF.dsk) disk image. Can I copy the format program from the 330Kb images? Or will it not format the 1.5Mb drive?
Wayne Parham
 
Posts: 240
Joined: March 18th, 2022, 3:01 pm

Re: Altair 8800c build thread

Postby AltairClone » June 12th, 2022, 12:33 pm

COPY.COM is on the disk and will perform disk format, verify, and duplication. Note, however, that formatting isn’t actually required if you want to create new disks by copying.

See https://deramp.com/downloads/altair/sof ... ReadMe.pdf

Mike
AltairClone
Site Admin
 
Posts: 632
Joined: April 5th, 2013, 10:55 am

Re: Altair 8800c build thread

Postby Wayne Parham » June 12th, 2022, 6:02 pm

Thanks so much, Mike! Just what I needed to know.

That's a great utility for this configuration. You've just done so much to round-out the system and make it complete in various configurations.

I wish Ed Roberts could see what you've done with his baby. He would be touched and impressed, I'm sure of that.
Wayne Parham
 
Posts: 240
Joined: March 18th, 2022, 3:01 pm

Re: Altair 8800c build thread

Postby Wayne Parham » June 15th, 2022, 9:06 pm

I have a little more progress to report.

With Martin Eberhard's help, I was able to get the rev. H 88-2SIOJP card working in my system. He was very responsive, and had me check my jumpers and switches. Just like Mike said earlier in this thread, Martin directed me to change the front-panel (sense input) switches after examining the start address and before toggling run. He even was willing to have me single-step through the instructions to see what was going on.

But nothing seemed to matter. I just wasn't getting any response on the RS-232 port.

Then - as part of the swapping in and out of the card cage to verify and set switches - on a lark I moved the SIO board into slot three, right beside the CPU and the front-panel interface. And that's when it started working!

I had been placing it somewhere around slot five or six. My typical setup had CPU in 1, FP interface in 2, FDC+ in 4 and SIO in 6. That works great when the rev G. board is installed.

So I decided to move stuff around and see what it did. The rev. G board can go anywhere. Slot 3 through 9. All slots work. But the rev. H board can't go past slot 4. And when it's installed, the FDC can't be placed very far away either. I haven't tried all combinations - or really even very many - but I can tell that the rev. H board makes the system more sensitive to board placement.

At least, that's the case in my 9-slot system. I don't have any terminators installed, so maybe it would act differently if I did. And I'm sure it'll all act differently in the 18-slot system with and without terminators too.

So anyway, hope that's helpful to everyone.

While I'm on the subject, I took a few minutes to document the switch settings and jumpers for each of the boards. I was really only interested in a couple of configurations: (1) Boot from disk using the FDC+ loader, and (2) start from ROM using one of Eberhard's boards, e.g. Amon or BASIC. So below is a list of settings for each of those configurations.

There is nothing below that isn't already documented in the manuals, but I found it helpful to make notes to tell me exactly what switches to set for each of my favorite setups.

======================================================================

For the settings described below, the switches set to "up"
or "on" are defined as "1."

To use Mike Douglas' disk loader at FF00, use these settings:

FDC+
S1 Ram - all zeros
S2 Rom - all ones
S3 Drv - 00000<drv>, so 00000100 for 330Kb or 00000101 for 1.5Mb

88-2SIOJP rev G
SW1 - 00011111
SW6 - 00000000
SW2 - 11011101
SW3 - 10000110
SW4 - Port 1 baud
SW5 - Port 2 baud

- or -

88-2SIOJP rev H
SW1 - 000000000
SW2 - 000000000
SW3 - 11011110
SW4 - 100000000
SW5 - Port 1 baud
SW6 - Port 2 baud

This will boot at FF00 and expose all the rest as RAM.

Boot procedure:

1. Stop / Reset
2. Set front-panel switches to 1111 1111 0000 0000
3. Toggle Examine
4. Toggle Run

======================================================================

To use Martin Eberhard's Amon on ROM (rev G board):

FDC+
S1 Ram - all zeros
S2 Rom - 01111111
S3 Drv - 00000<drv>, so 00000100 for 330Kb or 00000101 for 1.5Mb

88-2SIOJP rev G
SW1 - 00011111
SW6 - 00000000
SW2 - 11011101
SW3 - 00000110
SW4 - Port 1 baud
SW5 - Port 2 baud

This will start Amon at F800 and expose all the rest as RAM.

Startup procedure:

1. Stop / Reset
2. Set front-panel switches to 1111 1100 0000 0000
3. Toggle Examine
4. Toggle Run

At the prompt, type "BO" to boot from disk. Or type "?" for a menu.

======================================================================

To use Martin Eberhard's BASIC on ROM (rev H board only):

FDC+
S1 Ram - all zeros
S2 Rom - 01111111
S3 Drv - 00000<drv>, so 00000100 for 330Kb or 00000101 for 1.5Mb

88-2SIOJP rev H
SW1 - 000000000
SW2 - 000000000
SW3 - 11011110
SW4 - 000000000
SW5 - Port 1 baud
SW6 - Port 2 baud

This will start BASIC at C000 and expose 48Kb RAM. Alternatively,
you can boot disk at FF00, also exposing 48K of RAM (and maintaining
BASIC in ROM).

Either way, you must start using the following method:

1. Stop / Reset
2. Set front panel address switches to the desired starting address (C000 or FF00)
3. Examine
4. Set all front-panel switches to zero (to boot from port 0)
5. Toggle run

======================================================================
Last edited by Wayne Parham on August 14th, 2022, 3:56 pm, edited 1 time in total.
Wayne Parham
 
Posts: 240
Joined: March 18th, 2022, 3:01 pm

Re: Altair 8800c build thread

Postby BillO » June 16th, 2022, 11:35 am

Strange, I have board position sensitivity on my system to.
BillO
 
Posts: 136
Joined: November 11th, 2020, 6:29 am

Re: Altair 8800c build thread

Postby toml_12953 » June 16th, 2022, 4:59 pm

Wayne Parham wrote:I have a little more progress to report.

With Martin Eberhard's help, I was able to get the rev. H 88-2SIOJP card working in my system. He was very responsive, and had me check my jumpers and switches. Just like Mike said earlier in this thread, Martin directed me to change the front-panel (sense input) switches after examining the start address and before toggling run. He even was willing to have me single-step through the instructions to see what was going on.

But nothing seemed to matter. I just wasn't getting any response on the RS-232 port.

Then - as part of the swapping in and out of the card cage to verify and set switches - on a lark I moved the SIO board into slot three, right beside the CPU and the front-panel interface. And that's when it started working!

I had been placing it somewhere around slot five or six. My typical setup had CPU in 1, FP interface in 2, FDC+ in 4 and SIO in 6. That works great when the rev G. board is installed.



Do you have power going to both edges of the backplane (near slot 1 and slot 9 or 18)? If not there could be a voltage drop that affects boards in the slots farthest from the power connections.
toml_12953
 
Posts: 297
Joined: June 7th, 2013, 12:54 pm

Re: Altair 8800c build thread

Postby Wayne Parham » June 16th, 2022, 9:22 pm

You know, I haven't looked at the traces on the 9-slot board. So I don't know. I'll check it tomorrow. It's the board from s100computers.com, and power is connected through a Molex connector.

But in that computer, the power connector is nearest to slot 9, and when the system is finicky - when the rev. H 88-2SOIJP board is installed - I have cards installed in slots 1 - 4. It doesn't work if I space 'em out every couple slots.

I did see the original Altairs had power run as you've described on the 18-slot backplane. I have one of those too, but I haven't started focusing on it yet. I've put all my energy into the 9-slot version for now.
Wayne Parham
 
Posts: 240
Joined: March 18th, 2022, 3:01 pm

Re: Altair 8800c build thread

Postby AltairClone » June 16th, 2022, 10:41 pm

Wayne, try these changes on the FDC+ and rev H 2SIOJP in the configuration for running BASIC. See if it changes anything about where you can place the 2SIOJP in the motherboard.

FDC+
S1 Ram - all zeros
S2 Rom - 0100 0000 (PROM disabled, RAM ends at C000h)
S3 Drv - 0000 0<drv>, so 0000 0100 for 330Kb or 0000 0101 for 1.5Mb

On the 2SIOJP, disable both the “status disable” and the “phantom disable” options. After making these changes, let me know if this changes anything about board placement options.

If the above changes make no difference, then move ove J18 from “8080” to “Z80” and see what that does.

Mike
AltairClone
Site Admin
 
Posts: 632
Joined: April 5th, 2013, 10:55 am

PreviousNext

Return to Altair 8800c

Who is online

Users browsing this forum: No registered users and 4 guests

cron