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View Full Version : Zeta SBC - Minimal, self-contained, N8VEM compatible Z80 SBC



sergey
December 5th, 2011, 02:14 PM
Zeta SBC is an easy to build Z80 computer, that I've designed this summer. It was pretty popular on N8VEM list and I sold out all the PCBs. Now I am considering to reorder PCBs. Perhaps people on this forum will be interested to build this system? (If yes - reply to this post :-))

Here are the specifications:
- Small form factor (170 mm x 100 mm, 6.7" x 4"), can be mounted under a 3.5 floppy drive.
- CPU: Z80 (tested with NMOS and CMOS versions, up to 20 MHz, 6 MHz is required to support 1.44MB floppies)
- Memory: 512 KiB SRAM (system + RAM disk), 512 KiB flash (BIOS, CP/M, ROM disk)
- 8255 PPI. Can be used to connect an IDE hard drive or CF card using PPIDE, or for generic I/O
- 16550 UART - Console serial port
- FDC9266 floppy disk controller, supports common (that is IBM) diskette formats.
- RTC
- Runs CP/M 2.2, ROM images are available from N8VEM Wiki

More documentation is here: http://n8vem-sbc.pbworks.com/w/page/44366173/Zeta%20SBC

Update:
Tentative prices: PCB - $20, FDC9266 - $5, Shipping (one PCB and FDC - USPS First Class mail, no tracking) is $2 in US and $5 anywhere else.

Thanks,
Sergey

7270

7271

glitch
December 5th, 2011, 02:31 PM
Neat! I'd be interested in one!

commodorejohn
December 5th, 2011, 02:50 PM
I'd definitely be interested.

Tor
December 6th, 2011, 05:26 AM
I am interested.

-Tor

barythrin
December 6th, 2011, 07:26 AM
Pretty neat little rig! Do you know roughly the cost of the components? I see the part listing but was curious if you already knew a ballpark figure.

sergey
December 6th, 2011, 02:19 PM
Pretty neat little rig! Do you know roughly the cost of the components? I see the part listing but was curious if you already knew a ballpark figure.

I did some calculations, and it looks like all the components for the entire system will cost about $100 (including shipping).
If you buy all components (except PCB, FDC and PPI) at Mouser, get PCB and FDC from me, and find 8255 PPI somewhere else for $5, it will cost $88.76 without shipping.
If you buy some components at Unicorn Electronics (logic ICs, UART, connectors, and capacitors are cheaper there, they have PPI too), and the rest from Mouser, it will cost about $75 without shipping.

commodorejohn
December 6th, 2011, 02:25 PM
Couple of questions:

Is there a PLCC-to-DIP converter I can use for the Z80? I've got a 10MHz part laying around that's just begging to be put to use... ;)

I assume standard PC floppy drives will work? With a standard twist-cable, can I use two?

sergey
December 6th, 2011, 03:09 PM
Couple of questions:

Is there a PLCC-to-DIP converter I can use for the Z80? I've got a 10MHz part laying around that's just begging to be put to use... ;)

I assume standard PC floppy drives will work? With a standard twist-cable, can I use two?

You can build PLCC-to-DIP converter yourself using 40 pin DIP and 44 pin PLCC socket, some wires, and a hot glue to hold everything together (I built a 32 pin one when I was younger and had to reprogram a laptop BIOS). But I don't think it worth the trouble... 10 MHz Z84C00 in DIP package costs about $4. It looks like DigiKey has some adapters, but I bet they will be more expensive than $4 :-)

Standard PC floppy drives work with a twisted cable. For a single floppy you don't have to use twisted cable, just use the second device (it should be possible to recompile BIOS so it will be the only device, if you like).

Update:
Found one at eBay: http://www.ebay.com/itm/NEW-Universal-PLCC44-DIP40-Programmer-Socket-Adapter-Converter-Module-/260898823796
Make sure to verify that it has the proper pinout.

Soupwizard
December 7th, 2011, 07:42 PM
I'm in for at least one also! What the confirmed order count you need to place the order?

sergey
December 8th, 2011, 12:29 AM
I'm in for at least one also! What the confirmed order count you need to place the order?

I will be ordering PCBs regardless of the order count, but I would like to have an approximation, so will order enough PCBs for everyone.

NobodyIsHere
December 8th, 2011, 03:13 AM
Zeta SBC is an easy to build Z80 computer, that I've designed this summer. It was pretty popular on N8VEM list and I sold out all the PCBs. Now I am considering to reorder PCBs. Perhaps people on this forum will be interested to build this system? (If yes - reply to this post :-))


Great Job Sergey! This is a wonderful SBC that is well designed and appealing. Very impressive work!

Thanks and have a nice day!

Andrew Lynch

ajacocks
December 8th, 2011, 10:25 AM
I'm interested in a PCB and an FDC.

MikeS
December 8th, 2011, 11:35 AM
Most excellent documentation!

Is the software also documented somewhere?

Can it be downloaded without jumping through the Subversion hoops?

Is CP/M ready to go, i.e. stick it into the ROM, connect a console terminal and press RESET?

What, if anything, is the diskette format compatible with?

commodorejohn
December 8th, 2011, 11:47 AM
Does the ROM have a monitor and/or boot-from-disk function?

sergey
December 8th, 2011, 01:01 PM
Most excellent documentation!

Is the software also documented somewhere?

Can it be downloaded without jumping through the Subversion hoops?

Is CP/M ready to go, i.e. stick it into the ROM, connect a console terminal and press RESET?

What, if anything, is the diskette format compatible with?

The software (BIOS) is mostly written by Wayne Warthen. I don't think there is much of documentation (other than source code comments). But Wayne usually is pretty responsive, so you can try asking him on the N8VEM list.

The stable firmware image, including BIOS, CP/M, and also source code and compilation tools and scripts (in case you want to modify something) is available for download from N8VEM Wiki.
The firmware also includes a monitor derived (and shared with) N8VEM project that can do all the basic stuff monitors do - analyze and change memory content, do I/O operations, etc.
Also there is a subversion repository, that is something new, and mostly used for developing new features.

If the power-on reset circuit works (which it usually does) you don't even need to press the RESET :-) Just connect the terminal and plug in the power cable.

Diskettes are formatted using IBM PC compatible format (9 sectors/80 tracks for 720 KB and 18 sectors/80 tracks for 1.44 MB) and can be read / written on PC using programs like RAWRITE.

sergey
December 8th, 2011, 01:01 PM
Does the ROM have a monitor and/or boot-from-disk function?

Yes it does both.

Soupwizard
December 9th, 2011, 09:43 AM
I will be ordering PCBs regardless of the order count, but I would like to have an approximation, so will order enough PCBs for everyone.

Ok, then sign me up for 2 PCBs and 2 FDC9266s.

sergey
December 12th, 2011, 11:41 PM
An update and a question:
- I re-ordered PCBs, I should have them in 15 days or so.
- I will be ordering FDC9266 floppy disk controllers. Together with them I can order following ICs used in Zeta SBC (price is approximate, I will have exact one once I submit the quote):
Z84C0020PEC (20 MHz CMOS version of Z80 CPU) - $5
TMP82C55AP-10 (10 MHz CMOS version of 8255) - $4
SST39SF040-70 flash chips - $4 (I will program them with the latest firmware)
Anyone wants to get any of these ICs?

Tor
December 13th, 2011, 02:01 AM
I would like (in addition to the PCB) also one of those FDC chips, and the Z80. (I would actually like to get all of those you list, but I have to be a bit careful because if the total value w/o shipping goes above (at current exchange rates) approximately $33 I suddenly get to pay nearly $40 extra, in VAT and customs handling charges.)

-Tor

ajacocks
December 13th, 2011, 04:28 AM
I am interested in all 3 ICs.

Thanks!
-Alex

commodorejohn
December 13th, 2011, 08:30 AM
I'd be interested in all of those chips.

Soupwizard
December 13th, 2011, 09:06 AM
[edited, I got the count of chips and total $ wrong]

I'll also go for the "4 chips and a board" combo package. So my pre-order is now: 2 x "4 chips and a board" combo

Sounds like a drive-thru fast food order:
"May I take your order?"
"Uhh, I'll have two of the '4 chips and a board' combo, with the pre-flashed roms, to go"
"Your total will be $76 plus shipping. Please drive through."

sergey
December 14th, 2011, 02:42 PM
[edited, I got the count of chips and total $ wrong]

I'll also go for the "4 chips and a board" combo package. So my pre-order is now: 2 x "4 chips and a board" combo

Sounds like a drive-thru fast food order:
"May I take your order?"
"Uhh, I'll have two of the '4 chips and a board' combo, with the pre-flashed roms, to go"
"Your total will be $76 plus shipping. Please drive through."

Yeah, it sounds like a fast food order :-) Perhaps I should start doing kits instead. Like get the PCB alone or get the PCB and all four ICs. But some people have vintage Z80 CPUs and other things in their collections that they want to put in use.

Soupwizard
December 14th, 2011, 11:56 PM
Yeah, it sounds like a fast food order :-) Perhaps I should start doing kits instead. Like get the PCB alone or get the PCB and all four ICs. But some people have vintage Z80 CPUs and other things in their collections that they want to put in use.

Hmm, due to an impulse purchase on ebay (thye were cheap!), I have 120 Z80 2.5 Mhz CPUs, plastic dip-40, new old stock in tube. I was wondering what to use them all for...

Too bad 2.5Mhz is too slow to handle the floppy drive though. Say, your BOM says 8Mhz is needed for 1.44MB floppy use - how about for a 5.25" 360KB drive?

mnbvcxz
December 15th, 2011, 01:06 AM
Most users of the Nascom 1 computer ran the Z80 at 4Mhz even though it was a 2.5Mhz part.
Your chips may still be capable of running at 4Mhz, which is fast enough for DD floppy drives.
I am not sure about this but I think you can attach an HD floppy drive to a DD controller as you would an 8" DD drive.

sergey
December 15th, 2011, 08:59 AM
Hmm, due to an impulse purchase on ebay (thye were cheap!), I have 120 Z80 2.5 Mhz CPUs, plastic dip-40, new old stock in tube. I was wondering what to use them all for...

Too bad 2.5Mhz is too slow to handle the floppy drive though. Say, your BOM says 8Mhz is needed for 1.44MB floppy use - how about for a 5.25" 360KB drive?

360 KB drives use the same transfer rate as 720 KB drives (or 1.44 MB drives with 720 KB disks) - 250 Kbit/sec. So it will require the same CPU speed. But as mnbvcxz mentioned, 2.5MHz Z80 CPUs can be overclocked to 4 MHz without much difficulty. In fact I tested the board with a couple of Z80 CPUs (not 4MHz Z80A) running on 4 MHz and it worked perfectly.

I would recommend using 3.5" drives, they are less power hungry, and require only 5 V. Also they integrate nicely with the board. 1.44 MB drives will work with 720 KB floppies. And actually you can format 1.44 MB floppies to 720 KB, you'll need to cover the "high density" hole with a piece of adhesive tape.

mnbvcxz
December 15th, 2011, 12:58 PM
8" drives used 500Kbit/sec and you used a faster clock fed into the FDC, I think if you did this you could read/write in high density (1.44MB) or maybe 1.76MB like Amiga, but a 4Mhz z80 may not be fast enough on its own, you may need DMA.

sergey
December 15th, 2011, 01:23 PM
8" drives used 500Kbit/sec and you used a faster clock fed into the FDC, I think if you did this you could read/write in high density (1.44MB) or maybe 1.76MB like Amiga, but a 4Mhz z80 may not be fast enough on its own, you may need DMA.

FDC itself is capable of doing either 250Kbit/sec or 500Kbit/sec, but since the system doesn't have DMA, a faster CPU is required to support 500Kbit/sec transfer rate.

rcoley
December 17th, 2011, 01:15 PM
I'd be interested in a board and all components.

thx

sergey
December 27th, 2011, 03:21 PM
Hi,

Today I received Zeta PCBs and components. And I am ready to send them to builders.

Prices:
Zeta SBC PCB: $20
Z84C0020PEC (CMOS Z80 CPU, 20 MHz): $5
SMC FDC9266: $5
TMP82C55AP-10 (CMOS 8255 PPI, 10 MHz): $4
SST39SF040 (512 KiB flash, programmed with RomWBW v1.3): $4
Shipping, USPS First Class mail for 1 PCB + 4 ICs: $3 in US, $6 anywhere else. (Other options like tracking or registered mail are available per request)

I accept PayPal. Please send me a private message for payment details.

For builder's convenience I created two project lists on Mouser with almost all components for Zeta:
TTL ICs based: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=e8d3041c19
CMOS ICs based: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=25905e147c
Note that lists include 10 MHz Z80 CPU and 10 MHz oscillator and don't include FDC and PPI ICs. You might want to delete the CPU and choose different CPU oscillator frequency.

Thanks,
Sergey

commodorejohn
December 27th, 2011, 04:15 PM
Ah, cool, I'll order from you as soon as I can :)

Tor
January 10th, 2012, 01:28 AM
Hi,
For builder's convenience I created two project lists on Mouser with almost all components for Zeta:
TTL ICs based: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=e8d3041c19
CMOS ICs based: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=25905e147c

I haven't bought anything from mouser before so I have no previous experience with them. The project list stuff is great though. So I made my own variant of the CMOS variant list and tried to order two sets of that (to have some spares, etc.). During that process their web page said that it was well above the price to get free international shipping via fedex or ups, but at checkout there was only the option USPS and paid shipping. So I put it on hold for now (there were anyway a couple of items out of stock, and I had to find a replacement for the reset button which had suddenly changed to 8000 minimum order).

Anyone else with mouser experience (international shipping?)

-Tor

sergey
January 10th, 2012, 08:52 AM
I haven't bought anything from mouser before so I have no previous experience with them. The project list stuff is great though. So I made my own variant of the CMOS variant list and tried to order two sets of that (to have some spares, etc.). During that process their web page said that it was well above the price to get free international shipping via fedex or ups, but at checkout there was only the option USPS and paid shipping. So I put it on hold for now (there were anyway a couple of items out of stock, and I had to find a replacement for the reset button which had suddenly changed to 8000 minimum order).

Anyone else with mouser experience (international shipping?)

-Tor

Hi Tor,

I personally didn't use international shipping, but when shopping locally in US on checkout Mouser's web site gives a selection of different shipping options.

One person from Australia left positive feedback on Mouser's service, but apparently he did pay the shipping. See this thread here (in the middle):
http://groups.google.com/group/n8vem/browse_thread/thread/5ee7f8078b33342b

Regarding reset switch, some people already complained about this problem. Fortunately there are multiple replacements (even at Mouser). Please read this thread (closer to the end):
http://groups.google.com/group/n8vem/browse_thread/thread/d6637260035dadfa

Mouser is not the only source for the components. I found it convenient because they have almost all components needed from my projects. But obviously there are many others. For example DigiKey, Jameco are popular in US. Also there are some smaller distributors, like Unicorn Electronics. Finally you might find some components in your local electronic parts stores (in US they are tend to be more expensive and have less selection than online distributors, but usually they do have most of 74LS chips).

Zeta SBC was designed to use common and widely available components. I think all components (except FDC9266) are or were produced by multiple manufacturers. Also some components can be substituted with functionally similar ones: for example TTL 74LS logic with TTL 74ALS or 74F or CMOS 74HCT or 74AHCT.
Although it might be trickier with electromechanical parts, but even here some substitution is possible:
- Reset switch: replace with some another 6 x 6 mm right-angle tactile switch, like C&K PTS645Vxxxxxx or Omron B3F-3xxxx. Or it can be omitted at all, and some alternative reset switch can be connected to P2 (or just short P2 terminals with a screwdriver :-))
- Standoffs: Can be replaced with 20 mm - 25 mm long 3 mm screws and some plastic spacers.
- P6 (polarized header): Can be replaced with regular 2x1 header. But take care to verify the polarity in this case.
- Battery holder: Zeta uses battery holder with 20 mm spacing between leads (some have 20.1 mm, but will fit too). This is a very popular format, used by almost all computer motherboards.
- Stacked LEDs indicator: Available from few manufacturers, but it can be replaced with regular 3 mm LEDs, just bend leads at 90 degrees. The HALT LED (bottom one) is mostly for diagnostics purposes (it's fun to see it flashing then using FDTST in interrupt mode), and can be omitted.

I also have some substitution information on the Zeta's Wiki page: http://n8vem-sbc.pbworks.com/w/page/44366173/Zeta%20SBC#BOM

Thanks,
Sergey

Tor
January 11th, 2012, 12:21 AM
Thanks Sergey.
I'll look into the options and those threads you linked to.
BTW the PCB and chips arrived yesterday, all in good order! :)
-Tor

runni
January 23rd, 2012, 09:48 PM
Hello,
i'm interested for a PCB, did you have one PCB for me?
wich price and shipping costs to Germany?
PayPal?

Other Parts, FDC... and so on, is on stock. ;-)

Many thanks,
Ralf Neumann

sergey
January 23rd, 2012, 11:40 PM
Hello,
i'm interested for a PCB, did you have one PCB for me?
wich price and shipping costs to Germany?
PayPal?

Other Parts, FDC... and so on, is on stock. ;-)

Many thanks,
Ralf Neumann

Hi Ralf,

Your question is right on time :-) I received a new batch of PCBs today.
The PCB is $20, FDC and CPU are $5 each, PPI and flash (preprogrammed with BIOS, CP/M and some utilities on ROM disk) - $4 each. That is $38 for the entire package.
Shipping to Germany is $6. Please send PayPal to skiselev:gmail/com (replace ':' with '@' and '/' with '.')

Thanks,
Sergey

jutt
March 6th, 2012, 09:01 PM
hello forum;

hello sergey, just sent you an email to order. thanks.

commodorejohn
March 15th, 2012, 01:52 PM
Well, I just put in an order for the remaining parts for mine off the Mouser parts list (hooray for tax refunds!) I just had a few miscellaneous questions:
Any recommendations for a power adapter for this thing? I need something that can safely power the board and two 3.5" floppy drives. (Speaking of floppy drives, are there pre-existing cables that can connect the two-pin power connector on the board to four-pin floppy connectors, or do I have to make my own? If I do, do I wire the two of them in series, or in parallel?)
It looks from the datasheet for the UART like, combined with the provided oscillator, it can manage up to 115.2 kbaud, but the documentation says the BIOS default is 38.4 kbaud. Can a 20MHz Zeta SBC go up to 115.2? 38.4 should be plenty for my purposes, I'm just curious.
How does the memory mapping work? It looks to my inexpert eye like it's 32KB paged RAM and 32KB paged ROM (since it's Z80 I'm assuming the ROM goes in 0x0000-7FFF,) but I see there's a ROM disable as well. What goes in its place, if it's disabled?

sergey
March 15th, 2012, 03:37 PM
Well, I just put in an order for the remaining parts for mine off the Mouser parts list (hooray for tax refunds!) I just had a few miscellaneous questions:
Any recommendations for a power adapter for this thing? I need something that can safely power the board and two 3.5" floppy drives. (Speaking of floppy drives, are there pre-existing cables that can connect the two-pin power connector on the board to four-pin floppy connectors, or do I have to make my own? If I do, do I wire the two of them in series, or in parallel?)
It looks from the datasheet for the UART like, combined with the provided oscillator, it can manage up to 115.2 kbaud, but the documentation says the BIOS default is 38.4 kbaud. Can a 20MHz Zeta SBC go up to 115.2? 38.4 should be plenty for my purposes, I'm just curious.
How does the memory mapping work? It looks to my inexpert eye like it's 32KB paged RAM and 32KB paged ROM (since it's Z80 I'm assuming the ROM goes in 0x0000-7FFF,) but I see there's a ROM disable as well. What goes in its place, if it's disabled?

Use a regulated 5V power supply. For two floppy drives I would recommend getting at least 2 amperes PS. Pay attention to the wire length and gauge, so that you won't have too much voltage drop on it. This is especially important when using power brick/wall wart with a long DC cable attached to it. It is a good practice to use two separate pairs of wires for board and for disk drives. If you're planing to build a case, you can use an enclosed power supply such as Jameco #323282 (Mouser and probably others sell similar power supplies). An AT or ATX power supply also will work. You'll need to build the power cable yourself, you can find the plug part number in the BOM (note you'll need to get the female connector and two contacts for it, they are sold separately). You can scavenge floppy connectors from an old PC power supply, purchase one of these Y splitter cables with two floppy power connectors (e.g. http://www.pchcables.com/6in525to235y.html), or order the connectors from some components distributor.
You're right, with 1.8432 MHz oscillator UART will support rates up to 115.200 kbps (and even more with higher frequency oscillator). I think 20 MHz Z80 will work with 115.2 kbps just fine (4 MHz is fast enough for 38.4), but it might depend on particular software. Default BIOS uses polling mode, but interrupt driven mode is also possible. Also the 16550 UARTs have a FIFO, that might help on higher transfer rates, and it is enabled by default in newer firmware.
Your observation is correct. The Z80 64 KiB address space is split into two 32 KiB pages. The upper page is always mapped to the top 32 KiB of RAM. The lower page can be mapped to any area of ROM or RAM, depending on the content of the memory page select registers. Clearing bit #5 (~ROM_ENA) in the ROM Page Select Register (CFG2), enables ROM, and the ROM page is selected using bits #0 - #3 of CFG2. Setting bit #5 of CFG2 enables RAM, and RAM page is selected using bits #0 - #3 of RAM Page Select Register (CFG1). So that after a reset or on power up, the first page of the ROM is mapped to the lower 32 KiB (which contains the bootstrap code).


Just wondering, what do you want to use your Zeta for?

P.S. You've got me scared with the tax refunds. I thought that I missed the submission deadline. Anyway thanks for reminder, need to prepare my tax reports...

commodorejohn
March 15th, 2012, 04:02 PM
Okay, thanks. I might see if I can find a mini-ATX power supply. As for using it, mostly I just want something to play around with CP/M on, though combined with one of my nice amber terminals it might make a decent word processor ;)

bubbo
March 17th, 2012, 01:08 AM
Hi Yes
I would be interested I am in UK.

Brian

sergey
March 18th, 2012, 10:52 AM
Hi Yes
I would be interested I am in UK.

Brian

Hi Brian,

I replied to your e-mail.

Thanks,
Sergey

joerg
April 2nd, 2012, 07:04 AM
Hello,

I'am intrested in 2 PCBs + one time the 4 ICs to build a ZETA SBC.
What are the complete price with shipping to Germany?

regards joerg

lafleur
July 16th, 2012, 04:55 AM
a low cost power supply for Zeta and others...

$7.95 5V 4A

http://www.bgmicro.com/5v4aregulatedlaptoppowersupply.aspx

ajacocks
July 16th, 2012, 05:46 AM
That would have been a lot cheaper than the one I used.

By the way, I completed my build of the Zeta some time ago, and it's a really neat SBC. I (and several others) have posted photos and build notes on the N8VEM wiki, at:

Main page: http://n8vem-sbc.pbworks.com/w/page/44366173/Zeta%20SBC
Photos (more in other users' directories): http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder&param=Alex%20Jacocks

There's a new accessory board, called the ParallelPortPropellor, which provides VGA output, PS/2 keyboard, SD card storage, and a speaker. It is described here, and boards can be ordered from Sergey:
http://n8vem-sbc.pbworks.com/w/page/52472959/ParPortProp

- Alex

commodorejohn
July 16th, 2012, 08:30 AM
I got my board all soldered, I just haven't gotten the power supply finished (going for an AC plug & switch + power supply, as I'd rather not waste outlet space with another wall-wart, and I plan on putting this thing in a little case anyway.)

sergey
July 16th, 2012, 09:19 PM
I got my board all soldered, I just haven't gotten the power supply finished (going for an AC plug & switch + power supply, as I'd rather not waste outlet space with another wall-wart, and I plan on putting this thing in a little case anyway.)

You can use an enclosed power supply like this (5V/3A, $11.95):
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_1919043_-1

3A should be more than enough for Zeta SBC with a floppy drive.

commodorejohn
July 16th, 2012, 09:25 PM
Yes, that's the one I bought; I just have to get it hooked up to the board and to the power socket/switch assembly properly.

commodorejohn
June 7th, 2013, 06:44 PM
Okay, the completed board has been sitting around my apartment for way too long, and it's about time I got it all hooked up. I'm not quite clear on the last few details re: hooking up the power, though. As was suggested, I've got a Meanwell RS-25-5 and an AC plug/switch assembly. It's obvious that + and - on the SBC should go to V+/V- on the PSU, but it's not very clear which of the holes for the power plug V+ and V- are. Moreover, is one of them a separate ground? Does that need to be connected to the ground line on the PSU, or does the ground line on the PSU go to the ground blade on the AC plug?

Also, is there a good simple hack that could be done to add a simple timer interrupt to the system? I've been toying with the idea of building this into a homebrew MIDI sequencer/workstation, but that would require a reliable clock source...

sergey
June 7th, 2013, 11:28 PM
Hi,

Power connector: The center (pin) of the power connector is +5V, the sleeve is ground (or -). You can use a multimeter to verify the polarity of your power supply before you connect it to the board. There is no separate ground.

Timer interrupt: I can't think about anything really simple. I guess you can connect a timer to /INT line through a 74LS06 open collector inverter. You can reuse the 74LS06 inverter gate that was intended for FDC, since BIOS doesn't use interrupts for FDC I/O. For timer you can use 8254, or Zilog Z80 CTC, or a simple impulse generator, for example a frequency divider fed with UART's 1.842 MHz frequency. If using a programmable timer it also will need to be connected to a system so you can program it. It might be connected either directly to Z80 bus, or through 8255 PPI (if you're not using it for ParPortProp or PPIDE).

commodorejohn
June 8th, 2013, 12:01 AM
Well, I mean which of the three holes in the board is +5V and which is ground; I didn't get a barrel connector since I was just planning on wiring it directly to the PSU (eventually I plan to put it all together in a case.)

sergey
June 8th, 2013, 10:04 PM
Two of three pads are connected to the ground. You can actually find what pad is +5V and what pads are ground by looking at the traces. for example capacitor C29 connected between +5V and ground, and has polarity marked.

commodorejohn
June 8th, 2013, 10:07 PM
Okay. That's what it looked like, but I'm no expert at reading schematics or traces, so I wanted to be sure, rather than hook up the power and find out I was wrong by the smoke :D

commodorejohn
June 9th, 2013, 07:01 PM
Pleased to report it's up and running :) The cramped little connector array on the AC plug/switch assembly gave me more soldering trouble than the board ever did! But once that was all taken care of, it powered right up without issue, talks happily over the serial port, and boots into CP/M. Now I just gotta get working on a case...

sergey
June 13th, 2013, 08:06 PM
Congratulations!

Post some pictures (especially the case :-))

commodorejohn
June 13th, 2013, 08:36 PM
Will do :D

jibanes
December 25th, 2013, 10:25 PM
Sergey,

I pm'd you with an order, thank you.

Jerome

commodorejohn
February 26th, 2014, 02:34 PM
Is there a simple way to get a custom build of the system ROM? I'd like to get VDE configured for a VT-100 emulation, and I'd also like to ditch some of the unnecessary files (the IDE stuff, for example) and put some other miscellany on the ROM disk in its place...

sergey
February 26th, 2014, 03:03 PM
Yes, you can build a custom ROM yourself.

Here is the folder with the RomWBW: http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder&param=RomWBW

Get RomWBW.zip, unzip it, and read Doc/Build.txt, it describes the build procedure. In case you have any questions about build process or firmware at all please ask fine folks at N8VEM group.