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| Re: Mini MC68040 [message #4650 is a reply to message #4648] |
Tue, 24 April 2018 21:36   |
ale500
Messages: 44
Registered: April 2018
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The idea with the bus sizer is a very good one. It seems a bit difficult to get or it is very expensive. If only used for an 8 bit bus to an E(E)PROM, a cpld would do. One has to issue 4 reads, latch the data and then present a full 32 bit read, some clocks later and to assert TA. It sounds simple. I have some XC9572XL that could do that.
Edit: I was fiddling a bit with the bus buffers and I could replace the 4 buffers with 2 XC9572(XL) and use them for the bus sizing too. I have to see if the logic would fit, these CPLDs are not that big, nor that fast.
[Updated on: Wed, 25 April 2018 00:18] Report message to a moderator |
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| Re: Mini MC68040 [message #4664 is a reply to message #4663] |
Thu, 26 April 2018 20:36 |
plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA
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ale500,
I'm glad you are thinking about the 68040 SBC. I afraid I don't have much time to participate in the discussions. Here are some unorganized thoughts I have:
* There is a conceptual design of booting 68040/68360 off a byte wide EPROM. You'll need an I/O coprocessor anyway. 68360 is a good I/O candidate and this concept is interesting:
https://www.nxp.com/docs/en/application-note/AN2035.pdf
* If you use 4x EPROM, use 5V flash (e.g. 29F040) that allow you to reprogram them in-situ.
* You need to worry about heat sink + fan. 68040 is quite a power hog, heat sink is required. Even 68LC/EC040 needs heat sink & fan.
* 4 layer pc board is the baseline board design. This plus relatively expensive 68040 CPU means cost control is out of window. One can reasonably design & build 68030 based SBC for $40 or less thus do not require crowd funding, but 68040 SBC will be $150-$200. Count on 2 design iterations and half a dozen qual units and you are talking about a significant investment. An coordinated effort is needed to realize it.
* 5V SIMM72 DRAM is available up to 128meg. It is a good fit with the 68040. A simple DRAM controller takes a dozen flip flops to implement in CPLD.
* Be sure to connect D24-D31 to devices with interrupt vectors. This is different than 68000 which expects interrupt vectors from D0-D7.
* When I designed the 68040 in the early 1990's, I used Altera's EPM9560 which is the biggest 5V CPLD I'm aware of at the time. It may still be available, but costly, no doubt. I may be wrong but I don't believe Xilinx has 5V CPLD anywhere near that size.
* If you can find 3.3V 68040 then you'll have much better (& cheaper) selections of parts. I don't believe 3.3V 68040 is available in PGA, however. Some surface mount components are required in any case.
Good luck!
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| Re: Mini MC68040 [message #10586 is a reply to message #4666] |
Sun, 04 February 2024 05:49 |
plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA
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Senior Member |
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I am working with forum member mikesmith on a support board for a commercial 68040 mezzanine board (IP940). So I'm rekindling my interests in 68040. What is the status of the mini-040 project?
Bill
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