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Zeta SBC - Minimal, self-contained, N8VEM compatible Z80 SBC

Soupwizard

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Feb 2, 2008
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Vancouver, WA, USA
[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."
 
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sergey

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[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

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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

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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

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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.
 
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mnbvcxz

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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

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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.
 

sergey

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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
 
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Tor

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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

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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 SBC#BOM

Thanks,
Sergey
 

Tor

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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

Member
Joined
Sep 5, 2004
Messages
23
Location
Germany, Munich
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

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Jul 15, 2010
Messages
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Silicon Forest, Oregon, USA
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

New Member
Joined
Mar 7, 2012
Messages
1
order

order

hello forum;

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

commodorejohn

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California, USA
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

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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

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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 ;)
 
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