The first is a modified version of the ZX Spectrum 128 editor. A call to the TEST routine in ROM-1 is replaced with code to reset the Timex ULA.
The second is an exact copy of the original ZX Spectrum BASIC but has TR-DOS traps in place of the character set (
0x3c00 to 0x3fff is filled with PUSH AF: RST 8: NOP: NOP).
This makes the machine more compatible with existing software titles than the original ZX Spectrum 128. A third page is exactly as the same as the first and a fourth page is exactly the same as second, but without TR-DOS traps (it has the character set). The A15 line of EPROM is connected to /M1 of Z80, while the A14 is connected to bit 3 of the 0x7ffd port latch. The TR-DOS traps allow emulation of TR-DOS by the ZXVGS operating system. Custom ROMs can be loaded into memory and paged into place using the DOCK or EX banks. Jarek has fitted an external NMI button for ROMs with a working NMI routine.