JJLUCSY@MTUS5.BITNET (08/16/90)
I presently own a Tandy 1000TL(yes, I know, bad choice) which has a 286 but an 8-bit bus. As far as I can tell, the thing won't switch into protected mode. I was running VMIX which would've put it in protected mode, but the thing locks If I tell it to not to switch, it works fine. I also experienced the same effects when running Windows 2.somethingoranother. Does anybody have any ideas why? Is this a hardware problem? or software? or is my machince going nuts? Any help would be GREAT! Joel Lucsy | My computer IS intelligent! JJLUCSY@MTUS5.BITNET | It even has temper tantrums!
grege@gold.GVG.TEK.COM (Greg Ebert) (08/16/90)
Real vs Protected mode ---------------------- After a reset, the 80286 is in REAL mode, which makes it look like an 8086. Setting the PE bit causes the 80286 to enter PROTECTED mode. Now you're stuck there. Thanks Intel ! So, the kludge-nuts at IBM decided to let the keyboard controller yank on the reset line to force a change back to REAL mode. What does all this mean ? Perhaps the Tandy system doesn't have the necessary hardware to emulate a reset via the keyboard controller. If you like to tinker with hardware, make a circuit which pulses the reset line when a hex 'FE' is written to I/O port 64h. Actually, you want to detect a binary 1111xxx0 being written to port 64h. My guess is that your 286 is entering protected mode, but can't get back into real mode because the hardware kludge is missing. If you think THIS is ridiculous, you should hear about GATE_A20 !!!
rcollins@altos86.Altos.COM (Robert Collins) (08/20/90)
In article <1301@gold.GVG.TEK.COM> grege@gold.GVG.TEK.COM (Greg Ebert) writes: >Real vs Protected mode >---------------------- > >What does all this mean ? Perhaps the Tandy system doesn't have the necessary >hardware to emulate a reset via the keyboard controller. If you like to > >My guess is that your 286 is entering protected mode, but can't get back into >real mode because the hardware kludge is missing. > You want to reset the '286 without using they keyboard controller? Try this: HOSE_IDTR DQ 0 RESET_286 PROC LIDT HOSE_IDTR mov ax,0 mov ds,ax lodsb RESET_286 ENDP Guaranteed, that will reset the '286. -- "Worship the Lord your God, and serve him only." Mat. 4:10 Robert Collins UUCP: ...!sun!altos86!rcollins HOME: (408) 225-8002 WORK: (408) 432-6200 x4356