cbmeeks wrote:
The fastest through-hole EEPROM I can find is 70ns and 128K. At least from Mouser.
70ns seems to be it with EEPROMs. EPROMs are somewhat faster: 55ns for UV-erasable parts like those I used in my POC units, or 45ns for OTP parts, which I've also tried.
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But what are you guys using that are running 4 MHz, or 8 MHz or even 20! MHz?
I don't use EEPROMs at all, and POC V2 inserts one wait state when ROM or I/O is selected in order to support 20 MHz operation. The highest speed at which I've been able to reliably run with a 55ns EPROM is 12.5 MHz. I did get POC V1.1 to boot at 15 MHz with an OTP ROM, but the SCSI host adapter couldn't keep up.
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I guess SMD would open the doors to faster components.
Packaging usually doesn't factor into device speed, at least not in the sort of parts we routinely use in our systems.
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I'm really wondering if it would be easier to get some 12ns SRAM and just load it at startup with a micro-controller..then mark it read-only if I needed to.
You could do the same with an EEPROM. However, it might be a challenge designing a circuit built solely with discrete gates that will run fast enough and have enough logic to know when to wait-state, as well as be able to shadow ROM into RAM. This is where programmable logic makes sense.