IBM 770 manual System/2 and Personal Computer BIOS Interface, 0061, 2-31

2. Reset the system microprocessor by writing a 1 to bit 0.

3.Issue a Halt instruction to the system microprocessor.

4.Reenable all maskable and nonmaskable interrupts.

If you do not follow this procedure, the results are unpredictable.

Note: Whenever possible, use BIOS as an interface to reset the system microprocessor to the real mode. For more information about resetting the system microprocessor, referIBM toPersonalthe

System/2 and Personal Computer BIOS

Interface.

System		Control Port		B	(Hex		0061)
Bit	definitions		for		the		write		and	read functions of this port are shown
in	the	following		figures:
		Bit	Function
	7–4		Reserved
	3		Enable		channel		check
	2		Enable		PCI	SERR#
	1		Enable		speaker		data
	0		Timer 2 gate to speaker
Figure		2-31. System		Control		Port		B	(Hex	0061, Write)
		Bit	Function
	7		PCI SERR# (PCI error) status
	6		Channel		check status
	5		Timer		2 output
	4		Toggles with each refresh request
	3		Enable		channel		check
	2		Enable PCI SERR# (PCI error) check
	1		Enable		speaker		data
	0		Timer		2 gate		to	speaker

Figure	2-32. System Control	Port B	(Hex 0061,		Read)
Bit 7	If a system	board	error	occurs		and the PCI SERR# line is
	activated, this bit		is set	to	1.
			System		Board	2-31