schematic

I corrected one error, previously there were 2 bits mixed up:

=== Cut ===

The proposed modification can be easily carried out on
computers KAY, PENTAGON, SCORPION and others not assembled on PLM.
She allows you to use Spectrum memory much more efficiently
than just through one 16kb page in the processor address space.
The number of pages is increased to four and they cover all 64kb of memory
addressed by the Z80. Any memory bank within the first 256kb can
be included in any processor memory window. The rest of the memory is addressed
as before. Within the first 256kb, programs
operating with large amounts of data and frequently used data can be located.
memory above 256kb can accommodate programs that are content
with a 16kb code and data segment (for example, device drivers) or disk cache,
ramdisk...

Maybe 256kb is not enough, I don’t know if it’s worth complicating the circuit too much?

All these computers with RAM from 128kb and above have
a 7FFD port that controls switching memory pages in the window with address C000.
Circuit design of the memory manager in different On computers there is little difference: there is a port decoder, a 555TM9 register and a 555KP11 multiplexer. The presence of the 555KP11 microcircuit makes it easy to carry out
modifications that may often be requiredonly 1 microcircuit.
You will need to disconnect pin 15 of the 555KP11 microcircuit from the board, it will
be used to switch modes. You also need a configuration control port
(for example, in Scorpio or Kai you can use 1FFD,
you will only need 1 bit set when resetting to 0 and never
set to 1 by TR-DOS programs. You will also need one inverter.

DIAGRAM:

D47 is microcircuit 555KP11 computer memory manager
SCORPION, “yellow board”. For other computers, using the diagram
you need to clarify the correspondence of the contacts of the 555KP11 microcircuit and the signals
D0, D1, D2, D4 of the data bus D48 pin 9 - write signal in port
7FFD. "yellow scorpion", available on all computers on pin 9
of the 555TM9 chip...

SPECTRUM BUS
┌──┬──────┐ connects to D47
D4 >──────15──┤D0│ RG │ output:
D2 >───────1──┤D1│ Q0├─10───> 12
D0 >───────2──┤D2│ Q1├─9────> 9
D1 >───────3──┤D3│ Q2├─7────> 7
├──┤ Q3├─6────> 4
A10 >──────14──┤W0│ │
A11 >──────13──┤W1│ │
wr7FFD >──────12──┤WR│ │
(D48/9) ├──┤ │
A14 >───────5──┤R0│ │
A15 >───────4──┤R1│ │
┌──11──┤OE│ │
│ └──┴──────┘
│ 555ИР26
│
└──────────────────┐
│
enable ┌──┐ │
extended. >──────┬───────┤1 o────┘
addressing │ └──┘
by log. 1 │ ЛH1
└────────────────> D47 pin 15 (CS)

!!!! There is also some way to turn off the ROM!!!
In different computers this is done differently

I don’t specifically write how the extended addressing mode will be turned on
and how the ROM will be turned off. On different machines this
can be done or has already been done in different ways.

PROGRAMMING VIA PORTS
┌──────────┬────────────┬────
│ PORT │ 73FD │ 77FD │ 7BFD │ 7FFD │
├──────────┼────────────┼────── ─────┼───────────┼────────────┤
│ BITS │ │ │ │ │
│ 0 │ R0-0000 │ R0-4000 │ R0-8000 │ R0-C000 │
│ │ │ │ │ │
│ 1 │ R1-0000 │ R1-4000 │ R1-8000 │ R1-C000 │
│ │ │ │ │ │
│ 2 │ R2-0000 │ R2-4000 │ R2-8000 │ R2-C000 │
│ │ │ │ │ │
│ 3 │ screen 5/7 │ screen 5/7 │ screen5/7 │ screen 5/7 │
│ │ │ │ │ │
│ 4 │ R3-0000 │ R3-4000 │ R3-8000 │ R3-C000 │
│ │ │ │ │ │
│ 5 │ LOCK │ LOCK │ LOCK │ LOCK │
│ │ │ │ │ │
│ * 6 │ R3-C000 │ R3-C000 │ R3-C000 │ R3-C000 │
│ │ │ │ │ │
│ ** 7 │ R4-C000 │ R4-C000 │ R4-C000 │ R4-C000 │
│ │ │ │ │ │
└──────────┴────────────┴───── ──────┴───────────┴─────────0 * Bit 6 is used only in PENTAGON computers with more than 128kb of RAM
** Bit 7 is used only in KAY or PENTAGON
computers with more than 256kb of RAM.

The number of the addressed memory bank is calculated using the formula:

n
___
\
/__ (Rx)*(2^x) ; n=2..8 (depending on the type of computer).
x=0 ( 128..8192kb )

Setting the LOCK bit to 1 blocks ports 7xFD for writing.

Ports 73FD, 77FD, 7BFD, 7FFD are used to install the memory bank recorded
in them to addresses 0000, 4000, 8000, C000 respectively.

The selected ports are equally decrypted in all common
SovietZX-SPECTRUM clones as a 7FFD port. All possible conflicts
are associated only with switching to the extended mode, which can be implemented in different ways on different
computers.

Modification in most cases is useless for TR-DOS programs.
The benefit will be enormous when used in an operating system
that can allocate memory between different programs or
parts of a program, it also becomes possible to implement
real multitasking with programs of real (>64kb) size,
but again you need an appropriate operating system, but not
a tape recorder emulator.

If something is unclear or you have suggestions - write:

Kirill Frolov 2:5030/82...@fidonet.org
2:5030/946...@fidonet.org
500:812/1.507@zxnet
500:812/23.25@zxnet

P.S.: Everything has already been done and is working. Buying 555IR26 on the radio market in St. Petersburg is no
problem.

=== Cut ===

* Crossposted in REAL.SPECCY
* Crossposted in ZX.SPECTRUM

On August 27, 2000, you wrote here:

[...]
...

KF> but again you need an appropriate operating system, but not
KF> a tape recorder emulator.

...

KF> P.S.: Everything has already been done and is working. Buying 555IR26 on the radio market in St. Petersburg
KF> is not a problem.

We are waiting for the “appropriate” OS... For a long time. :-\

All the best.
Roman.
[ZX]

KF>> St. Petersburg is not a problem.

RM> We are waiting for the “appropriate” OS... For a long time. :-\

Not that long ago. Only this axis will not be :-(