There is an Australian dinosaur called the Ozraptor. Its fast - maybe not the fastest dinosaur - but fast enough to catch a mere human, should a mad scientist decide to revise the species.
It seemed a fitting name for my latest eZ80 module. Introducing the ozRaptor, and its specifically designed high speed memory module.
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The goal of this new module is to enable the eZ80 CPU to be able to access RAM at the eZ80’s full speed. Remove the need for the CPU to slow down when it is accessing the external RAM (ie: wait states).
The original 2MB linear RAM module, using through-hole SRAM chips AS6C4008, operating over the RCBus, is just not able to keep up with the eZ80. As such, for the eZ80 to use this memory module, it needs to slow down memory access (ie generate wait states when reading and writing to the memory).
The RCBus was never designed to operate at the speed the eZ80 needs. Specifically, the rise and fall times of the various digital signals an eZ80 generates causes numerous signal integrity issues. As the voltages switch from ground and 5V, a lot of ringing and reflection noise is generated, preventing reliable operation.
So a new, specially designed memory bus interface is required to enable the eZ80’s true performance to be achieve.
So I designed two new modules. The ozRaptor and the associated high speed memory module.
This new high speed RAM modules has a 78 pin keyed connector. The connector has the 24 address lines, 8 data lines and a few control signals. The rest of the lines provide lots of ground return paths. These ground pins, combined with the fact the memory is connected directly to the eZ80, ensure all the digital noise issues are resolved, and allow the eZ80 to operate at and beyond its full speed.
In my testing to date, I have achieved a full 4MB of RAM (2 modules of 2MB each) accessed by an overclocked CPU of 30Mhz, with absolutely no wait states.
The memory module is designed around four 10ns SRAM surface mounted chips (CY7C1049GN-10VXIT - 36-SOJ). Despite these being surface mounted and not through-hole, they are not very hard to solder with a conventional soldering iron.
I have some short videos of the soldering approach I use on the main page - 2MB Fast Linear SRAM.
The ozRaptor module uses the same eZ80 CPU module designed for the original eZ80 for RC module.
Now the eZ80 can finally stretch it legs. Run free and munch on some humans - armm - I mean code!
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