Additional notes I (Cesar Hernandez) got talking with Gerton Lunter:

Q: I assume your interface had 32 kB of ram, which you maped in the rom space

A: "Yes, that’s right; I used a static 32k ram chip that I mapped into the 0-16kb range, twice.  One bank contained a modified copy of the original rom, the other contained the extensions mentioned in that bit of text."

Q: But what about the shadow 32 k ram? I suppose this is where you stored the ramdisk and the screen buffers... But where does it come from? My guess is that you enabled the "unused" 32kb ram on all spectrums 48kb (the known story about Clive Sinclair buying  64kb defective chips, which only used half of the chip). So... do you enabled that “defective” half chip for your samram?

A: "And yes, I indeed used the unused 32k bank of dynamic ram chips.  The original spectrum used defective chips (to cut costs, always a major focus of Clive Sinclair it seemed).  My own spectrum was a bit younger, and at that time I suppose not many chips were defective, so they just put regular chips in - mine had no bad bits."
"

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So, samram has 32kb of static ram than can be mapped on rom address (0-16383), and also uses 32kb of ram (from the unused defective chips) than can be mapped on 32768-65535

I assume the 32kb of static ram preserve its contents after shutting down the machine. 
In ZEsarUX, I treat these 32kb as if it were a rom, needs to be loaded from disk and can not be written


Also, I discovered some new opcodes (only emulated, not real Z80 opcodes of course) that are used on Samram:

-EDF9:

LD A,(DE)   (from samram rom)
LD (HL),A 
INC E 
INC H

-EDFA:
RAMBANK LD A,(HL)
Not 100% sure:

if (HL<32768) normal read
if not, read unmapped ram block:
-if mapped normal ram, read shadow ram
-if mapped shadow ram, read normal ram

-EDFB:
RAMBANK LD (HL),A
Not 100% sure:

if (HL<32768) normal write
if not, write to unmapped ram block:
-if mapped normal ram, write to shadow ram
-if mapped shadow ram, write to normal ram

-EDFE:
ROMPOKE HL,A

Poke to normal ram



