An old project that started in the 80 'an interesting hardware interface
to expand the ram at 'inside of the spectrum specifically talk about expansion ram 80Kbyte for Sinclair ZX SPECTRUM 16 / 48k.
The module allows for RAM expansion from 80k to increase a portion of memory in the zx spectrum 48k off some hardware limitation.
We do a bit of light on any points in order to better understand its operation.
Why do we need this circuit and cause some memory of zx spectrum and 'it has been disabled?
Initially in the original design of the spectrum they were implemented DRAM 64K
These special semi-conductors had but a factory cost quite relevant.
Secondly, they could be handled entirely by the mathematical processor Z80ACPU from 3.5MHz which we know only works in 8-bit.
In practice the internal interface Z80 would not be able to handle all the memory of 64k
So according to the thought of Sinclair Research use of ram 64K he meant squandering of material that would not be used completely.
For this reason therefore the electrical circuit of the zx spectrum were used DRAM specially underpowered or fallate only use 32K.
In this way the Sinclair bought at half the price of the faulty modules to use them only in the lower (Low Level).
We wonder at this point if it is 'for this reason that the failure to' inside of the spectrum are mostly relocated to the memories of ram? most likely YES.
Memories TMS4532 OKI3732 we find today on most zx spectrum we could consider them as surrogates bought at a good price.
This should be remembered and 'needed to respond to the demands and characteristics correttamete processor mathematical Z80ACPU that can not handle memory 64k entirely ie is both high level and low level.
Today we can throw in this situation .... relocating this portion of RAM to 'inside of the spectrum.
And 'you can with this little circuit (removable) enable two virtual pages 32K swappando software with the command OUT instruction
When activating this portion of the ram in the 'area preddisposta and' you can begin an experimental very attractive through all existing software.
We are faced only to 'start of a long process of experimentation and knowledge.
For now, however, we are content to study at the level of all the effects of routine experimentation, as well as Utility video games. It will provide many surprises ...
It must be said that at the time were developed the routines specific to make the most of this ram,
but you can understand that now find one or two routines and dedicated 'mission impossible as it's been 30 years.
The request for this project was started from some programmers complained that the ability of the ram now limiting in just 48k. We are limiting the development of some Utility you started getting more and more complex
There was therefore a need for a device that could ingombente you to increase available memory.
And an immediate need to work better and to 'give greater performance
to the need of users ..