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From: grege@gold.GVG.TEK.COM (Greg Ebert)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Problems with 286 in protected mode
Message-ID: <1301@gold.GVG.TEK.COM>
Date: 16 Aug 90 16:05:25 GMT
References: <90228.001800JJLUCSY@MTUS5.BITNET>
Organization: Grass Valley Group, Grass Valley, CA
Lines: 19

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 !!!