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CP/M

MEMDISK

IDEDOS

Macface2 for ZXVGS

Introduction

Macface2B is an external interface with:

2kB EPROM, paged in #0000..#07FF;
16kB SRAM, paged in #0800..#3FFF (or #0000..#3FFF when EPROM is deactivated);
3 bits write only port at #7B address (A2=0 and A7=0);
NMI button with noise eliminator;
configuration switch (can disable memory and port);
through slot with /ROMCS

The EPROM contains modification of ZXROM.

jump to #04AA in NMI service (after PUSH AF:PUSH HL);
SRAM activation at #04AA with jump to #0800;
turbo for tape saving and loading (constants in #05??..#06?? code).

The #7B port is zeroed at reset. The meanig of its bits:

bit	when =0	when =1
0 (switch up)	both EPROM and #7B port are active	the EPROM is disabled
0 (switch down)	both EPROM and #7B port are disabled	the EPROM is disabled
1	SRAM is writeable, when is activated	SRAM is write-protected
2	only EPROM can repleace ZXROM	activates SRAM that repleaces ZXROM where the EPROM doesn't

The Macface cannot be activated on reset with ZX128, because after reset the ROM0 is activated and the code doest switch to ROM1. In this case:

deactivate interface (switch down),
after menu appears, select ZX128 BASIC
type USR0
activate interface (switch up).

Upgrade

The interface doesn't work with ZXVGS versions with software switching, so it can be used only with PLD and TMX ones, where the #0008 address is catched by hardware.

The modification includes:

repleacing 2kB EPROM with 4kB EPROM - the low 2kB has standard contents, the high 2kB has new contents;
using free D latch to swith EPROM halfs as bit 3
repleacing turbo tape code with calls to ZXVGS (RSX entries).