Hi, Havent played anything hard on it to test if it is a valid 1802 but I have comments and suggestions. Build it as a basic engine, if it needs ram then set a external parameter list for how much and what addresses, same for rom. Simulate IO, if it has a uart on the N-lines then create the registers/data you interact with (or the Q and Sense lines). The console can be like the ELF (switches and lights) and/or a RS232 tube connected via Q and F lines, software uart required as part of the code as UT4 does. Load UT4 (or whatever) from a start up list to emulate the rom and have the 1802 engine execute the "rom" cone out of memory space. This would allow code to "call" various ut4 routines like get or type. The miniassembler is nice and plenty handy. You may want to consider having it run like real code loaded into ram later on. The core of the instruction set is fairly regular so the select tree can be broken into functional sub trees for simpler code. The version of TB I have is quest TB and I don't have it on machine readable form (other than papertape which I currentlly can't read) so I'd have to copy the pages and someone can have the fun of toggleing it in, it'a about 1k or 2k. Allison On Wed, 3 May 2000, Mike wrote: