ZX Ferrum #00 09 января 2004

Железо

Iron - scheme virtaulnogo ROM.

                       Virtual ROM


(C) Demon / DPC


  One day, after the installation on his pentagon new firmware
(NeOS v1.00, Gluk Reset Service v5.3, TrDos v5.13f), I found
that the BASIC command PRINT 2 ^ 2 gives unexpected
Results (something like 0. 8232839109-e10). Down and Out the 
trouble started as they say, further studies have shown that 
the sign of the copyright deprived the bottom line in the test 
firmware NeOS Notdetectable Notdetectable and besides the same 
version is clearly not 1. 00, many things did not work. But 
most of all I killed that does not work is my favorite igruha 
Terminator 2, digging in the code, I found the binding to 
interrupt Basic128, but since there NeOS or Service is 
advancing bummer. 

  At that time there was one way to flash the ROM, but
this time we have turned down the Spectrum in the same town 
(and I Speck came in 1999) and people through which I pierced 
ROM is not enough that struck down with Speck, thallium and 
generally somewhere ejected. But in some a newspaper I read an 
article that mentions virtual ROM where the real ROM is 
replaced with a memory page, but not of the arrangement, and 
had to think for yourself. 

  I do not know how to look at the scheme of guy, but I got 
this: 


               TM2 KP12


     S1 ON 1oR May 2 S1

  0v D DD61 / January 14 S0 YA 7 DD18 / 5

               C

       OFF 4oS o6 0v 1 SA


                             6 A0

                        0v 5 A1

         LE1 / 1 4 A2

                             3 A3



                                KP11


                      / DOSEN 3 A0 4 DD61 / 3

                       ROM2 6 A1 7 DD61 / 6

                               A2

                               A3


                        A15 2 B0

                        A16 5 B1

           apply for a B2

              DD50 / 1 B3


           1 'S
DD50 / 1 0v 15 OE


          LI1 LL1


                     1 DD51 / 4

         DD51 / 4



         Figure 1. The scheme of the virtual memory (the 
Pentagon) 


  Signal LE1 / 1 memory expansion scheme the Pentagon and the 
Leningrad at 1mb Simm (was in some of the rooms DejaVu), ie, 
the multiplexer KP12 placed in the gap providing a signal bit 
at sample of addresses is less than # C000.


  Firmware loaded on the page # 31 - basic128, # 32 - dos, # 33 
- basic48.


  When it all worked, I was very pleased, began to jump,
clap (just kidding, it looked the part much more fun;)) and 
thought it would be nice to write a prog that would load the 
firmware. Well ... Well I did and wrote. It is in the annex to 
hrip archive there and firmware, which I have currently there 
and that I collect, so that if someone is flashing, that is not 
me, then send I will be glad.


  While the scheme is only available for the Pentagon.

  For all questions, please contact the publisher.