the venerable 80186 (and 80188)

While we're on the subject of 80186s I discovered some odd (well undocumented) behavior whilst experementing on my RM Nimbus (as I'm writing a MESS driver). If I load a value into AX, and then do an out instruction with AL, the whole of AX seems to still appear on the data bus, something like: MOV AX,055AAh OUT 022,AL It looks like to me that the whole of AX is actually getting put out, and that the /BHE ine is set to signify only the bottom 8 bits are valid. The Nimbus video controller seems to ignore /BHE and treat the data bus as always 16 bits wide. Is this known undocumented behavior ? I seem to remember that the Z80 has a similar undocumented behavior with the addressing of it's in and out instructions also. Cheers. Phill. -- Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric ! "You can twist perceptions, but reality won't budge" -- Rush.