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I have been working on designing a PCB for a Z80 computer that I plan to sell a few times for interested people. The Z80 will work at a maximum of 8 MHz and has parallel lines going to a system controller and an SRAM chip. The board is 170x110 mm in size. Currently I use 16 mil traces for the parallel bus and address lines and a spacing of 25 mil between them. I wonder whether this is enough for 5V data @ max. 8 MHz. Do I need termination resistors?

What do you think?

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  • \$\begingroup\$ Look at other Z80-based design of similar size, do they terminate the bus? I seem to recall that they don't, not at that speed. One reflection though, about your board size. 160 x 100 is the eurocard standard, and a lot of pcbs have that size, which could make it easier finding a case etc. Something to think about unless you actually need 170 x 110 for something else. \$\endgroup\$ – pipe Jan 17 '16 at 20:58
  • \$\begingroup\$ @pipe I will check some other reference designs. The one I used as a reference did not use any but the board was clocked slightly slower at 4 MHz and was wired on a perfboard. I try to get it to eurocard size which I tried initially, but the connectors required me to expand the board. Also I intentionally kept the parts non-smd and the chips all dual-inline-packages so they take up significantly more space than their SMD counterparts. But as I want to make it a kit, I will rather not use SMD. \$\endgroup\$ – Benedikt M. Jan 18 '16 at 0:09
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I think that's excessively big. I normally use 8 mil width and space unless there is a good reason not to, and I don't see one here.

8 mils is something just about any board house in the world can do, usually with a little extra margin so that nothing is being pushed to the limit. If you know the board house and that they can do finer line/space, then that's fine. Just realize that you may not be able to dump it on any board house, at least not for the lowest price. 6 mil width/space is still well within the capabilities of many processes. At 4 mil width/space you need to know the board house and that they can do it reliably, not just say they can do it.

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  • \$\begingroup\$ +1. 8MHz is not an high frequency and the limit is the fab, or your fantasy. \$\endgroup\$ – Vladimir Cravero Jan 17 '16 at 23:36
  • \$\begingroup\$ Thanks! I plan on using link for making my boards. Also I am glad my current figures will work and that I can even go below that. \$\endgroup\$ – Benedikt M. Jan 18 '16 at 0:06

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