Altair 8800 with Z80 CPU wont toggle anything. Help!!

[k1atn]

Hi, I finally wired up my Altair 8800 and put a California Computer Systems Z80 Model 2810 CPU board in it, as well as an S.D. Sales/Systems 4K Low power static RAM board in it. I then hooked up the display/control board, and fired it up. Well... The CPU boards Interrupt light is on as well as the front panel's INTE light, the MEMR light is on, the INP is dim, M1 is on, OUT is very dim, the WO the light is on, and the WAIT light is on. The lights for A0-A15 are on with all of them being a very tiny bit dimmer than normal. The Interrupt LED on my CPU board is lit up to as i will show in the picture on the bottom of the page. The problem I'm having is that I can't toggle in anything. I tried entering the sample program from the Altair operators manual, using the switches under D7-D0, and absolutely nothing happened. The reset switch is the only switch that does anything either besides the power switch. I'm new to the altair, so I may be doing something wrong so could somebody help me please?

Thanks.

Two pictures are of the front panel, and one picture is of the Interrupt LED Lit on the CPU board.

 

[Chuck(G)]

Have you debugged the front panel? The Altair 8800s are notorious for iCs going bad, particularly the plastic ones. Also, the power supply capacitors (particularly if you have the "A" supply) usually are dried out by now. A scope would be very handy for this.

 

[JDallas]

...The problem I'm having is that I can't toggle in anything.

Did you try SINGLE STEP switch in both positions?

You might try turning off RUN and stepping it through its initialization after a RESET. If you see it change state, SINGLE STEP to SINGLE STEP, that will tell you that at least most of the panel in running and then figure out WHAT the microprocessor is doing. As the LEDs are dimming, it might suggest that its running an interrupt polling loop... no real idea as I have no information on the Z80 board. It might have a power-on code insertion to jump to a ROM monitor (Like the Cromemco ZPU). That first command would be C3.nn.nn if I remember my Z80 machine code from the late 70s.

 

[k1atn]

Well, I've checked the capacitors, with an ocilloscope, and they're all in perfect working order , I at least got it out of what it WAS doing, and the deposit switch ONLY working and it now reads random data as my dad says, which shouldnt be as there is no data there. when i hit the switch it cycles through something???, i dont know what yet. it also looks like my address and data lines are mixed up, A0 is currently located at A4, and A1 is currently located at A5. so i'm hopefully going to fix that issue, as for the data lines being mixed up, my dad, who owned the altair before i did, said not to worry about for the moment. It still won't examine, run/stop or toggle things in yet though.

 

[k1atn]

JDallas, I cant use the RUN command or SINGLE STEP at the moment, they don't work. RESET was the only one that worked, but now the DEPOSIT and DEPOSIT NEXT does something but i don't think it's doing the right function, like i said my data lines and address lines are mixed up, the DEPOSIT/DEPOSIT NEXT switch isn't depositing, it's switching through the memory addresses, so maybe its acting like the EXAMINE/EXAMINE NEXT switch, so maybe that's one of the data lines that is mixed up.

 

[Corey986]

What is the exact power on procedure you are using?

Make sure you press stop and reset at the same time at least once to put the CPU in a known state before doing anything. Most people think you only need to press reset. Not true on the Altair for power up. You should do both at the same time.

 

[k1atn]

I don't know what you mean exactly by power on procedure, i just turn the unit on, and wait for it to try to set to ready, but what is happening is that as soon as I turn it on it starts reading from memory, and CONSTANTLY too, or so my dad says, he also says it's trying to execute a program, but as far as i know there's nothing in memory and also the on-board ROM on the CPU board that should contain the Moss 2.2 Monitor, is blank because the board had no ROM chip when i got it and i had to order one and i made sure it's the proper chip too. i have the .bin and . cue files, i just don't have an Eprom programmer that can interface with my computer because my programmer is from the 70's and it needs repairing anyway. i found out about the stop and reset at the same time thing when i hit run after power up and deposit didn't work anymore, i hit stop and reset at the same time and deposit worked again, but nothing else. but like i said the deposit switch is acting like the examine switch so when i say deposit worked or didn't work, i mean that it either cycled through memory when i toggled it or it did nothing.

Here's a little video of what i'm talking about, maybe it'll help. It shows me toggling all the switches on the bottom, individually except for protect/unprotect,also deposit (cycling) and then hitting run and then deposit (not working) then hitting reset and stop at same time then deposit (working again).

 

[Marty]

Hi All;
K1atn, You are sort of close, most likely as previously stated, yuou have some Ic's that are not goot or the solder need touching up, or a Bad switch..
As per the Stop and Reset, hold Your Hand, Palm down (I use my left, even though I am right handed), and place my first finger on the Stop/run switch and my thumb on the Reset switch..
I push up on the Stop Switch with my first finger and at the same time, while holding it up in the stop position, I then push the Reset switch with my thumb holding both for a second.. Release the reset first, then release the stop switch.. Sometimes You need to do this more than once..
Since it is a Z-80 Board, it might not this, but it is a good idea or good habit just to do it after first power up..
Also the D0-D7 on the cable are not wired D0 thru D7, the order is different.. I will later when I have time look it up..
You could have Bad Ic's on any of the Boards or on the Front Panel..

THANK YOU Marty

 

[glitch]

If you don't know the state of your CPU and RAM, you'll have to start with those. I typically start with a "HALT ROM" or by hardwiring a HALT onto the the bus with a protoboard. Having a known-working CPU is going to make debugging the front panel a lot easier.

 

[Dwight Elvey]

Your address problem sounds like you have the data wires
from the front panel plugged in upside down.
Oops! I see Marty mentioned that.
The front panel needs a working processor to do things.
C3 is used and can tolerate the D0 to D7 swapped with
D7 to D4 but it still does strange things.
Other swaps will not work right at all. Trace the wires
on the front panel to the processor.
Dwight

 

[k1atn]

Okay I just traced the wires, and 72 (PRDY) and 68 (MWRITE) were switched, 45 (SOUT) was in a hole that wasn't marked, and 54(EXT CLR) was on 45. So I fixed those and they are as they should be now. I then fired it up, and the stop/run, single step, and examine/examine next switches function again, as well as the deposit switch. But the computer still won't let me jump to an address, or deposit new data. and it's still currently reading random data.

Here's a video of what I mean.

https://www.youtube.com/watch?v=vmjJuXU16xk

 

[Marty]

Hi All;
K1Atn, You have made good progress.. You stated that both Examine and Deposit work, But, that is only Partially true, as Deposit will advance the Address, but it will not actually Deposit.. But, that Is still progress..
Also the D0-D7 on the cable are not wired D0 thru D7, the order is different.. Here is the correct order from Left to Right on the 8 or 10 pin Connector that plugs into the CPU Board.. D3, D2, D1, D0, D4, D5, D6, D7.. My Altair has a 10 pin connector, but only 8 are used..
Also, Could You post a Picture(s) of Each of the Boards that Your Machine has in it, such as the Z-80 CPU board, the Memory Board(s), the I/O (serial) board.. Also the Connector..

Here are some Pictures of what I have for Reference, they are the connector, 8080 CPU and Serial I/O Board and a converter connector for Altair to Imsai.. They may be Blurry, as I never know till I have uploaded them..





THANK YOU Marty

 

[k1atn]

Marty, I think my data wires are wired right. Reading the labels on the front of the display/control board where the wires connect, D7 is blue, D6 is yellow, D5 is red, D4 is black, D3 is grey, D2 is dark blue, D1 is the second yellow on my cable, and D0 is the second red. As i show in one of my pictures, the color pattern of the wires going into the socket on the CPU board match if you compare the color coding i mentioned above and match it to the labels right above the socket on the CPU board. Here are the pictures, BTW I don't have an I/O board yet. Also my front panel data connector on my CPU board is 16 pin but it only uses 8 pins for data as you can see in one of my pics.

 

[k1atn]

Here's the last picture showing what i was talking about with my wiring for my data lines. For some reason it only lets you post 5 photos per post. The reason the other wires are cut off is because i don't think i need them. it seems that in a z80 CPU board manual similar to my own it shows the wiring diagram for connecting it to a front panel display. 2 wires would connect to one spot on the display board (Wires 1, and 16=D0, wires 2, and 15=D1, ect. ect. which equals the 16 pin socket on the CPU board, but the way i see it, all i need is 8 pins, 8 wires so i use half the socket and therefore the other wires are cut off in the photo.

 

[Frank S]

I think my data wires are wired right...

I don't think so.
The order from the edge of the front panel PCB is: D7,D6,D5,D4,D3,D2,D1,D0
e.g. in your wiring D0 has a red color and is connected to D5 or D1 on the front panel.

Frank

 

[k1atn]

Yep, you're right. i have D0 and D1 switched. I'll fix that later today. As for the red being connected to D5, there are two red wires, one is connected to D5 and one is supposed to be connected to D0.

 

[Marty]

Hi All;
K1Atn, You have the Imsai style of connector, on Your Z-80 Board, so the 8 wires You have is correct, Just have to fix the Order, as Frank already stated..
Since You have a multipurpose Z-80 Board, which already has a Serial connection, (top Left hand Corner), You don't need another one for now..
Also, since it has an Eprom, installed as well and it might automatically be Jumping to that Memory Location, You would Not be able to use the Deposit/Deposit Next in that area of the Memory..
Also, You need to check that Your Memory Board is Addressed for Starting at '0000 and not some other address..
Once You have D0 and D1 fixed, Please let us know of any progress..

THANK YOU Marty

 

[k1atn]

Got the wires fixed, and they are as they should be now, Below is a picture showing exactly how i set the board up which is for the first 4k block. Also since you mentioned that it might be automatically jumping to the Eprom memory, what would happen if I took the Eprom chip out? Because originally when i got that board it did not have an Eprom installed, i went and bought one.

Thanks again for all your continuing help, it is very appreciated.

 

[glitch]

There should be an option for disabling power-on-jump to the EPROM on the CPU board. As I discovered with my Vector Graphic ZCB, disabling the feature may not entirely work as desired (the ZCB still asserts /PHANTOM, which will lock out some RAM boards). There are several different power-on-jump strategies common to S-100 boards, in my experience it seems like asserting /PHANTOM and mapping the internal EPROM socket to 0x0000 is the most common for CPU boards with integrated EPROMs.

 

[k1atn]

yeah i have the power on jump to Eprom as well as phantom enable jumper disabled. I took the Eprom chip out, just to see if there would be a change from it maybe jumping to Eprom memory. the chip is blank so i guess it wouldn't hurt the board anyway as the CPU board had no Eprom chip in it when i bought it to begin with. Still no change though.