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Anyone recognize this Apple ][ clone motherboard?
- Thread starter tgarnold
- Start date
SomeGuy
Veteran Member
Very nice. Does look homebrew. No idea about it, but I have read storied about people making home-brew Apple II motherboards back in the day. But I think those were usually clones of the Apple II / II+.
It really doesn't look all that Apple II-ish to me, aside from the 6502. Have you tried dumping the content of the ROMS?
It really doesn't look all that Apple II-ish to me, aside from the 6502. Have you tried dumping the content of the ROMS?
Eudimorphodon
Veteran Member
The HD46505SP CRT controller chip and what looks like 2K of dedicated SRAM likely serving as the video buffer argue pretty strongly against this being an Apple II clone. It’s a 6502 based single board computer with 8K of ROM, 16k of DRAM, and *probably* 80x24-ish text video output, but outside of that it’s pretty hard to guess what it was *for*.
g4ugm
Veteran Member
It looks like a commercial board as has what appears to be a part number and labelled links for ROM options, but home built as hand written labels on the ROMS and a wide range of date codes. I wonder if its worth perusing some of the mags of the day to see if anything pops up...
Eudimorphodon
Veteran Member
It could be something for embedded applications; not necessarily “home built” but too low production for mask ROMs.
Yes, it is most likely a commercial board. DIVO
In the photos that you provided; I cannot make out some of the semiconductors. So, to verify what's it is likely with reading the firmware Routens, I go by the picture that was provided.
I have seen similar PCB layouts that are close to it, So this is likely some type of a Data Terminal Video display board. Other item is an alarm monitor board/MCU unit.
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To follow this thought by:
2 of 8-pin chips, I can't make out part numbers. But if their Optical Couplers, AMP chips (being used as a line driver or receiver) by their PCB location.
Several 14-pin chips I can't make out part numbers. If any are a counter, shift register logic. (Then it is likely a Data Terminal Video display board).
The location of the DM 74193n
1 chip 20 pin I can't make out part number
1 chip 24 pin likely a DRAM refresh ctrl or could be a USART/MCU, Judging by its location.
The 40-pin IDC connector only has half the traces connected on the top. Probably uses a parallel keyboard with a couple of pins being used as a keyboard ID.
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In the past I have delt with Coaxial, Current loop base data terminals that have a similar PCB layout, as I have noted above the other possible options.
embedded applications like in an alarm monitor board/MCU unit has already been noted by user "Eudimorphodon"
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Hopefully this helps point you to the answer that you require.
In the photos that you provided; I cannot make out some of the semiconductors. So, to verify what's it is likely with reading the firmware Routens, I go by the picture that was provided.
I have seen similar PCB layouts that are close to it, So this is likely some type of a Data Terminal Video display board. Other item is an alarm monitor board/MCU unit.
..
To follow this thought by:
2 of 8-pin chips, I can't make out part numbers. But if their Optical Couplers, AMP chips (being used as a line driver or receiver) by their PCB location.
Several 14-pin chips I can't make out part numbers. If any are a counter, shift register logic. (Then it is likely a Data Terminal Video display board).
The location of the DM 74193n
1 chip 20 pin I can't make out part number
1 chip 24 pin likely a DRAM refresh ctrl or could be a USART/MCU, Judging by its location.
The 40-pin IDC connector only has half the traces connected on the top. Probably uses a parallel keyboard with a couple of pins being used as a keyboard ID.
..
In the past I have delt with Coaxial, Current loop base data terminals that have a similar PCB layout, as I have noted above the other possible options.
embedded applications like in an alarm monitor board/MCU unit has already been noted by user "Eudimorphodon"
..
Hopefully this helps point you to the answer that you require.
Bruce Tomlin
Experienced Member
I don't see any reason to believe that this is an Apple II clone. Just because the ROMs are labeled F8 F0 E8 E0 doesn't mean anything except that it uses 2708s. The Apple II has two more ROMS for D8 and D0. It has an RCA video connector, but it uses a big video chip instead of the TTL soup of the A2. And it seems to have 2114 for the video RAM, which means that video isn't being used for DRAM refresh, and there's no graphics mode. And of course no slots.
So it's just a random 6502 system, but a bit above average by using 16K DRAM. If you can dump the ROMs, it might be possible to identify where it came from. (But I understand if you can't dump them, as most programmers don't support them at all)
Compare with the clone that I have: https://forum.vcfed.org/index.php?threads/what-apple-ii-motherboard-revision-is-this.1239677/ which was enough of a clone that I asked for a version identification because I didn't notice the lack of Apple trademarks.
So it's just a random 6502 system, but a bit above average by using 16K DRAM. If you can dump the ROMs, it might be possible to identify where it came from. (But I understand if you can't dump them, as most programmers don't support them at all)
Compare with the clone that I have: https://forum.vcfed.org/index.php?threads/what-apple-ii-motherboard-revision-is-this.1239677/ which was enough of a clone that I asked for a version identification because I didn't notice the lack of Apple trademarks.
Eudimorphodon
Veteran Member
I'm kind of inclined to think it *could* be a smart terminal board. The one thing missing is an onboard serial chip, but that could live elsewhere and communicated with in parallel, or it's even *possible* it could be bit-banging it with a port on the 6821P. But it certainly doesn't *have* to be a terminal, it could be for driving a UI embedded in... gosh knows what industrial thing.
It has a HD46505SP on it, which is a Hitachi clone of the 6845. It doesn't really need any counters on top of that for video display.
Do you mean the 24 pin chip next to the four D2114A SRAMs? Pretty sure that's the character generator ROM.
How it does DRAM refresh is actually an interesting question. The 74153's next to the 4116s are clearly used for multiplexing the DRAM address lines. I wonder if it could be doing something sneaky like using the video addresses from the CRTC as the refresh counter.
It has a HD46505SP on it, which is a Hitachi clone of the 6845. It doesn't really need any counters on top of that for video display.
Do you mean the 24 pin chip next to the four D2114A SRAMs? Pretty sure that's the character generator ROM.
How it does DRAM refresh is actually an interesting question. The 74153's next to the 4116s are clearly used for multiplexing the DRAM address lines. I wonder if it could be doing something sneaky like using the video addresses from the CRTC as the refresh counter.
Bruce Tomlin
Experienced Member
Refresh could be as brute force as a having an IRQ run 128 NOPs out of RAM every millisecond.
Eudimorphodon
Veteran Member
Yeah, that's definitely a possibility in an embedded system.
Yes, I mean, In the picture I cannot make out the 24-pin chip part number only its date, so yes it could be a badly paced character generator ROM. Putting it there would add a cost to the PCB as the rest of the CRTC video support logic is elseware on the board. (Extra circuit traces).
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There are no photos of the boards bottom, so I can't conform if it's a character generator rom. If it is a character generator rom then the D2114 are likely used for the video ram. As there is 4 traces running between the two that is possible. This could also be an old 24-pin multiplexer chip or even a RTC or a NVRAM chip jugging by its location. (That is if this is a Coaxial or a Twinaxial data terminal device, then that could be a synchronous character buffer)
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Yes, they could be using the CRTC controller for the DRAM refresh, their where systems that did that.
Bit-banging or Bit-slice serial shifting is possible with this board, but with the rest on the unknown ics on board and no picture of its bottom side. who knows. Not all devices use a USART or Bit-banging for serial communication because there is some limitations in doing such.
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Without a picture of the bottom of this pcb, who knows how many more pins on the 40-pin IDC connector is used. It could have a XY input or have a parasail Address, date and control bus.
Eudimorphodon
Veteran Member
No, having the character generator directly adjacent to the SRAM chips is perfectly sensible; it’s the data output from the video RAM that drives the majority of the addressing. (You’re going to be using seven or eight bits from the SRAM for the character address, and only three or four bits from the CRTC for the row address.)
I can’t make out the number on the chip next to the 74LS273 next to the character ROM, but it could be the video output shift register.
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As for the DIVO marked on the board, the DIVO marking likely means Digital In(put) and Video Output.
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In the picture there is 18-pin D2114 a 4096 bit memory arranged in 1024X4 SRAM origination.
The dram is located closer to the CTRC controller then the SRAM (, I would have gotten shit for that waste of PCB and the extra traces needed).
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Two 8-pin connector The first one near the corner is possible for power.
----------------------- The second one has a 8-pin chip right next to it, so this is likely some type of I/O port (could be Serial i/o ?)
One 3-pin connector Likely has something to do with the video output by its location.
Composite video out Since the 3 pin connect is by the video output.
One 10-pin dip switch like used for some kind of board settings.
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If tgarnold has a composite video unit and a variable power supply, they could try to boot this board. But to go through a 10-bit address sequence just to see in the board displays anything would take some time to complete. The power requirements and its pinouts would be fairly easy to figure out.
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This PCB is using mostly 5-volt logics. Each 74lsxx chip requires about .08 ma @ 4.75 volt minimum and 5.25 maximum
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As I have noted on systems that must communicate in a none ANSI/ECMA serial communication standard they use a shift register for this purpose.
Higher data rates then Bit-banging and what is possible on some USARTS. Most ANSI/ECMA serial communication chips can only send and receive an 8-bit character with the control bits character in Async mode. To do a 12-bit or 16-bit character format you would have to do it in Sync mode and use a bit-slice Routen to reassemble or disassemble the characters extra length. No extra register programming information needed.
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Several really old Wangs with the Wang network, and AES Data systems, Some IBM Twinaxial and Coaxial clones also use a shit register for this purpose. At one time a 12-bit shift register was a lot cheaper than a USART chip.
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Hopefully the PCB owner will attach a scanned photo of the board bottom, as it would help us figure out what it was used for as the circuit traces on the underside would help identify its purpose. (As in where the run to).
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Unused useless as is Old PCB boards I use to test before I did component recover, so I wondering they got it from. If it was a business dump bin, that would help identify it (from the type of business it came from).
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In the picture there is 18-pin D2114 a 4096 bit memory arranged in 1024X4 SRAM origination.
The dram is located closer to the CTRC controller then the SRAM (, I would have gotten shit for that waste of PCB and the extra traces needed).
..
Two 8-pin connector The first one near the corner is possible for power.
----------------------- The second one has a 8-pin chip right next to it, so this is likely some type of I/O port (could be Serial i/o ?)
One 3-pin connector Likely has something to do with the video output by its location.
Composite video out Since the 3 pin connect is by the video output.
One 10-pin dip switch like used for some kind of board settings.
..
If tgarnold has a composite video unit and a variable power supply, they could try to boot this board. But to go through a 10-bit address sequence just to see in the board displays anything would take some time to complete. The power requirements and its pinouts would be fairly easy to figure out.
..
This PCB is using mostly 5-volt logics. Each 74lsxx chip requires about .08 ma @ 4.75 volt minimum and 5.25 maximum
..
As I have noted on systems that must communicate in a none ANSI/ECMA serial communication standard they use a shift register for this purpose.
Higher data rates then Bit-banging and what is possible on some USARTS. Most ANSI/ECMA serial communication chips can only send and receive an 8-bit character with the control bits character in Async mode. To do a 12-bit or 16-bit character format you would have to do it in Sync mode and use a bit-slice Routen to reassemble or disassemble the characters extra length. No extra register programming information needed.
..
Several really old Wangs with the Wang network, and AES Data systems, Some IBM Twinaxial and Coaxial clones also use a shit register for this purpose. At one time a 12-bit shift register was a lot cheaper than a USART chip.
..
Hopefully the PCB owner will attach a scanned photo of the board bottom, as it would help us figure out what it was used for as the circuit traces on the underside would help identify its purpose. (As in where the run to).
..
Unused useless as is Old PCB boards I use to test before I did component recover, so I wondering they got it from. If it was a business dump bin, that would help identify it (from the type of business it came from).
Yes, having the Character Generator ROM next to the Video RAM is sensible but the CRTC controller (HD46505SP) is located in the bottom left of the photo. If you have design high res graphics displays with the MC6845 then you know about the support chips needed, in this board layout that would use quite a few circuit traces on the bottom side of its PCB. (Thats all I was getting at).
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Anyways as I stated (noted) in messages, unfortunately theirs no photos of the bottom of this PCB, and theirs several IC I can't make out the part numbers to it.
Bruce Tomlin
Experienced Member
FIrst thing to do before trying to power it up is to map out where the voltages come from. The EPROMs and DRAMs want -5 and +12 volts as well as the obvious +5.
I'd still like to see those EPROMs dumped before anything else. That ought to tell almost everything.
I'd still like to see those EPROMs dumped before anything else. That ought to tell almost everything.
Eudimorphodon
Veteran Member
In short I think unless the OP comes back and volunteers more information about where this board came from and provides better pictures of certain parts of it (I mean, obviously we can’t really understand what’s connected to what with only half the traces) we’re pretty much stuck at ”definitely not an Apple II”.
I guess I’m just pretty skeptical about the theory that the SRAM is for some high speed comm application because it doesn’t look to me like there’s the parts for an attendant state machine to handle that function. There really isn’t much on this board, at all; the top row of chips is about enough to generate the needful clocks and pixel generation for this thing to “live”, full stop.
Who said anything about high res graphics? The 6845 was used for that, sure, and needed a lot of support circuitry when you wanted to do anything with color, etc, but for a simple monochrome character terminal the amount of additional parts is pretty minimal.
As for the placement of the CRTC, well, the video RAM *also* needs to be reachable by the CPU, so when you’re laying out your buses you will be flipping a coin at some point. Another point is the 6502 doesn’t have address bus tri-state so somewhere on the bus you’re going to need address bus demux to switch between the 6502 and the 6845. Coincidentally enough there’s a pile of demux chips right there next to both the 6845 and the 6502 in that corner of the board.
I guess I’m just pretty skeptical about the theory that the SRAM is for some high speed comm application because it doesn’t look to me like there’s the parts for an attendant state machine to handle that function. There really isn’t much on this board, at all; the top row of chips is about enough to generate the needful clocks and pixel generation for this thing to “live”, full stop.
Who said anything about high res graphics? The 6845 was used for that, sure, and needed a lot of support circuitry when you wanted to do anything with color, etc, but for a simple monochrome character terminal the amount of additional parts is pretty minimal.
As for the placement of the CRTC, well, the video RAM *also* needs to be reachable by the CPU, so when you’re laying out your buses you will be flipping a coin at some point. Another point is the 6502 doesn’t have address bus tri-state so somewhere on the bus you’re going to need address bus demux to switch between the 6502 and the 6845. Coincidentally enough there’s a pile of demux chips right there next to both the 6845 and the 6502 in that corner of the board.
In a previous message I also hinted about a EPROMs dumped (in directly), but may be the current board owner does not have an EPROM reader.
And yes, I did not post about the DRAM power requirements or the EPROM's power requirements, but you did. Thank you. But, with our posting the boards current owner haven't given us any feedback or response as of yet. So their purpose use of it ? unknown
And yes, I did not post about the DRAM power requirements or the EPROM's power requirements, but you did. Thank you. But, with our posting the boards current owner haven't given us any feedback or response as of yet. So their purpose use of it ? unknown
Eudimorphodon
Veteran Member
… that all said, an alternative theory I could be convinced by is the SRAM isn’t the character buffer memory, it could be for storing a user defined character set? There’s a certain attraction to that idea now that it’s popped into my head. If that is what it’s for its proximity to a character ROM still makes sense, and it also sets up the CRTC to be the source of DRAM refresh, sharing access with the 6502 on opposite sides of the clock.
I am not sure if the boards current owner can map out the boards power connections or not. They will have to look up the IC pinout and follow the traces back to the power connector. With us getting no feedback I not too sure if the board owners (has the skill to do such or if they want to do that).
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