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Nama
March 8th, 2016, 10:42 AM
Hi all,
Does anyone here use a SDSystems single board SB-200 using the SD monitor?

I have recently built up a 8 slot S-100 motherboard with the intent to use it with my SBC-200 board. I've never used this board before.
As far as I can tell my motherboard checks out, and all the voltages read ok.
I have plugged in the SBC-200, and I believe I have the jumpers setup correctly to boot from SDmon @ E000h. I see a reset pulse on the Z80, and I see CS lines on the E000h ROM pulsing. Other ROMs CS lines are all low. Have wired up the serial Tx, Rx and GND lines, but I can't seem to get the SDmon '.' prompt on my terminal, and it seems unresponsive to any input from said terminal.
Obviously this problem could be a lot of things, but I just wanted to talk to someone who knows this card so I could get an idea of what I should expect it to do. Just in case there is something in my setup (or the manual) that I'm missing or unaware of.

Thanks

Phil

MicrocomputerSolutions
March 8th, 2016, 01:22 PM
I have a SD Systems SBC-200. It's part of the first S-100 board set that I got running.

What are you using for a ram board? The SBC-200 isn't going to do much without one. It's been a while since I had the SD Systems board set stuffed in my mainframe, but it seems to me that you should get the "." on the screen as soon as you power the system and punch the reset button. I'd step into the other room and power up the board set if I had it installed in a mainframe, but the boards are sitting in a box, since I only have one running mainframe right now, and the Compupro is in it.

Do you have a RS-232 Breakout Box? You need to see if the serial Port on the SBC-200 is looking for handshake before it will send. I don't remember if it does, and I've been using a ribbon cable with all 25 lines connected.

I have the basic SD Systems board set: SBC-200, Expandoram II, and VersaFloppy II. All bought brand new in kit form, from Priority One Electronics (3 boards + SD Monitor PROM = $1000, plus sales tax) in the late 70's and early 80's. My first mainframe was a Integrand Research Model 800. I used the original Integrand Research (20?) slot motherboard initially without any termination installed. Later, I added a CCS Terminator/Extender Board to terminate the motherboard. The SD Systems board set seemed to run the same whether the motherboard was terminated or not.

I moved over to a Compupro components when I realized that I would struggle to expand my system if I stayed with SD Systems (SD Systems boards are not quite IEEE-696). I knew already that I wanted to add a modem, and a hard drive which was going to require more boards, and SD Systems was being slow at releasing a hard drive controller. The first board I bought after getting the SD Systems board set running was a Compupro Ram-17 64K static memory board. Never got it to run with the SBC-200 properly. Which is why I sent on to purchase the rest of the Compupro boards to build my second running S-100 System.

I'm using the SD Monitor, with CPM 2.2 and SDOS. The SD Monitor PROM I'm running was copied from a PROM that was purchased directly from SD Systems, not programmed from the listing in the manual. The copy of CPM 2.2 I'm running was also purchased from SD Systems and not altered from a Digital Research Distribution copy. Since the mid-80s, I pretty much only use the SD Systems board set as an advanced floppy disk drive tester. I hook freshly repaired and aligned drives to the SD Board set and run the Versafloppy drive diagnostics to make sure that the drives are 100% functional before returning to their owners.

Nama
March 8th, 2016, 03:13 PM
Hi MicrocomputerSolutions,
Thanks for the reply.



I have a SD Systems SBC-200. It's part of the first S-100 board set that I got running.
What are you using for a ram board? The SBC-200 isn't going to do much without one.


Ok, here maybe is my first issue. I was assuming the onboard 1k RAM (I believe it starts at F800) would suffice in running the monitor. I have a few RAM boards I could try, but I was trying to keep things simple to begin with.




It's been a while since I had the SD Systems board set stuffed in my mainframe, but it seems to me that you should get the "." on the screen as soon as you power the system and punch the reset button.


I have a Heathkit H19 terminal, pressing the terminals 'Reset' key alone does nothing. 'Shift' + 'Reset', resets the terminal, but testing the serial line with a logic probe during this keypress, I can't see any pulsing. Pressing other alphanumeric keys (A, B, C, 1, 2 etc.) I can see that these serial pulses are at least getting as far as the SBC-200 connector.
So, if the terminal doesn't send any data during the 'reset' keypress, then I'm not sure what this is supposed to accomplish. Please excuse my ignorance.
I also have an old 486 PC setup for most of my serial communications. I'd prefer to use this for testing the SBC-200 instead of my ancient H19. Do you know if it's possible to replicate this 'reset' key press on a 'modern' PC?



Do you have a RS-232 Breakout Box? You need to see if the serial Port on the SBC-200 is looking for handshake before it will send. I don't remember if it does, and I've been using a ribbon cable with all 25 lines connected.


No, I don't have a serial breakout box.
Ok, something to look into. As you say, maybe I need to connect a few more lines than just Tx and Rx and GND for serial communications to work correctly.
I think I will also pull the EPROM labeled SDmon, and really see what's on there.

Thanks for your time and support.
I'll do a little more probing over the next couple of days and over the weekend.

Cheers

Phil

glitch
March 8th, 2016, 05:08 PM
You probably want to be hitting reset on the S100 system, not the terminal. I believe reset on the H19 just resets the terminal itself. I don't know if the SBC-200 includes an onboard power-on-reset circuit, but if it does these often fail due to dried up electrolytic capacitors or partially shorted tantalum capacitors. Worth tracing out. Add a pushbutton reset if you don't already have one.

One of my first tests in troubleshooting a non-working serial line is to pull the UART and place a wire jumper in the socket between the Tx and Rx pins. If the terminal will echo then you at least know the cabling and level shifters are working.

Nama
March 8th, 2016, 05:30 PM
You probably want to be hitting reset on the S100 system, not the terminal. I believe reset on the H19 just resets the terminal itself.
Ah...yes, ok, that makes sense. Not sure why I was thinking the manual was talking about the terminal 'reset' key.

The 8 slot motherboard does have a reset switch. I did actually trying this, but it didn't result in a prompt on the terminal. I'll give it another go, now that I know this is what I'm supposed to do.



One of my first tests in troubleshooting a non-working serial line is to pull the UART and place a wire jumper in the socket between the Tx and Rx pins. If the terminal will echo then you at least know the cabling and level shifters are working.

Sounds like a good plan. I'll give that a go.

Thanks!

MicrocomputerSolutions
March 8th, 2016, 05:43 PM
Yep, resetting the terminal is not going to do anything. I meant reset/restart the SBC-200. Reset button on mainframe/motherboard very handy.

The SBC-200 has POC (can power-on clear, power on Jump, and power on reset).

Did you set the terminal communication speed on the H-19? My first standalone terminal was a H-19 that I built from the kit. The demand was so high for the H-19 kits when they were introduced that I was on a waiting list for like three months before I got my first one. You can turn handshaking off on the terminal, and test the terminal by bending a paperclip and sticking it into the RS-232 connector on the back of the terminal Pin #2 to pin #3. This will cause the terminal to echo whatever you type on the keyboard with the terminal on-line.

To keep the serial cable wiring simple, use a piece of 25 or 26 conductor ribbon cable with a 26-conductor edge card connector on one end, and a IDC (insulation displacement connector) RS-232 connector (don't use conductor #26, just peel it off short of the connector and cut off) on the other end.

Want to keep things simple? Don't bother trying to get old, low capacity, non-conforming, S-100 memory board to work with the SBC-200 (it isn't IEEE either). Get a SD Systems Expandoram II, try to get a fully populated 64K board (or an Expandoram III, with 1 bank (64K) or more, if you can find one) from an eBay Seller for about $80. There is a PAL on the board that limit/sets the amount of memory that can be installed on the board. Make sure that the PAL on the Expandoram II or III board you buy will support the full memory population of the board. You don't want to find out after you get the board that it will only address 32K (or some other nonsense). DO NOT BUY FROM SELLER: VINTAGECOMPUTERMUSEUM.

Nama
March 14th, 2016, 12:57 AM
Hi again,
So my logic probe died. Just one of those cheap Chinese ones, and it's the second one i've broken in as many years. Time to get something better I think.

Anyway, before the logic probe died, I was able to see that the Z80 didn't seem to get a reset signal. I traced back from the Z80 reset line through a 74LS14, and then to what I think is a pull up/down + debounce circuit, and then through the S100 bus to the reset button on the motherboard, which is connected to GND. The voltage of the 74LS14 input sits at at about 2.8V, and drops to 1.8V when the reset button is pressed. I don't see any change on the output of the 74LS14, and the Z80 reset stays high (~4.4V).

I tried another 74LS14, and still couldn't get a reset signal. I'm no electronics expert, so I'm not sure what going on here exactly.

Cheers

Phil

glitch
March 14th, 2016, 06:21 AM
If you can find a Tektronix P6401, they're an excellent logic probe.

That capacitor in the reset circuit is probably bad, or you'd see the input to that 74LS14 sitting right near 5V. The capacitor/diode/schmitt trigger combination is used to provide a lengthened and debounced reset signal and power-on-reset -- when the power supply is turned on, the capacitor is at 0V on its positive terminal, and charges through the 10K resistor to +5. Once it reaches the 74LS14's turn-on voltage, the system comes out of reset. Smacking the reset switch grounds the capacitor out and brings its positive terminal back around 0V, which puts the system back into reset. So a bad cap doesn't explain why the pushbutton isn't pulling that point really close to ground when it is pressed. Perhaps check the 220 Ohm resistor in series with the reset button?

FWIW, I've repaired a number of Vector Graphic ZCBs and every one had a bad reset capacitor, which would cause intermittent reset functionality, and sometimes even spurious resets!

MicrocomputerSolutions
March 14th, 2016, 09:31 PM
Does the motherboard feature active termination?

If it does, there would be a 5 volt regulator circuit on the motherboard. If I remember correctly, the IEEE-696 spec calls for the address, data, and control lines to terminate to 2.8V (the voltage I think you said you saw).

Many motherboard designs use a simple voltage divider (with pairs of resistors or SIPs on each line being terminated) to split the 5V from the regulator down to the 2.8V.

I'm going to be picking up a single-board computer featuring a ADC Super-Six sometime in the next few days. When I get it, I'll be able to plug my SBC-200 in and experiment with it. First I'll try running it without the memory board to see if it does anything with the Expandoram II pulled out. I've never tried running it that way, and you trying to run yours this way has peaked my curiosity.

Nama
March 16th, 2016, 06:46 PM
Thanks Glitch, I'm going to keep an eye out for a decent priced Tektronix P6401.
Looks like a nice unit.

I'll also check out the cap in the schmitt trigger circuit. You mentioned a diode. I can't see a diode in the circuit at all, either on the SBC-200 or on the motherboard side of things.
I have attached a partial (reset area only) schematic showing the SBC-200 (right) and the motherboard (left) combined into one image.

30155

Hi MicrocomputerSolutions,
Yes I believe the motherboard is terminated. I did solder in about 10 resistor networks, so I'm assuming that this is the termination.
I'll look into the voltage regulator/divider and see if that's where the 2.8V is coming from.
Let me know how you get on with your SBC just running off the built in 1k.
My fix is on hold for a wee bit until I can get a logic probe.

Thanks again

Phil

MicrocomputerSolutions
March 16th, 2016, 08:08 PM
I have two logic probes, both at least 30-35 years old. Neither one has ever given me any trouble. I thought you couldn't get any cheaper than the Micronta logic probe that I've used for hundreds (or thousands) of hours (mostly fixing floppy disk drive logic boards). I think I got it in the late 70s for like $10 (when I was working for Radio Shack). My "good" expensive one is a Global Speciaties "LP-1" (I paid about $20 for).

You don't have to spend much to get a working logic probe, they aren't much more than a few leds, a couple of switches and simple pulse trap and stretcher circuits.

glitch
March 17th, 2016, 04:04 AM
Oops, you're right, no diode on this one! Sometimes there's a diode to bleed off the capacitor's charge quicker when the positive power supply goes go ground.

Nama
October 10th, 2016, 12:06 AM
As it turned out the SBC-200 was working perfectly. However Don's 8 slot motherboard design does not produce the correct voltages to cause a reset on the SBC's Z80. Jumpering R18 in the reset circuit seems to produce the correct reset.

Also, for those wanting to know, and as I assumed, the SD Monitor can indeed run from the SBC-200 with it's 1K onboard memory only.

I'll be building this system up with a Versafloppy II card, Does any one happen to have a SDOS or CP/M disk image?

Thanks again.

Phil