Compaq MSB900L user manual MSR bit enables/disables into I/O

DIGITAL-LOGIC AG			MSB900/L Detailed Technical Manual V1.0
I/O Map	Continued…
I/O Addr.	Function	Size	R/W	Comment
3F1h	Floppy Status R B	8bit	RO	First Floppy.
3F2h	Floppy Digital Out	8bit	Shw@	First Floppy.
3F3h	No Specific Usage	8bit	---
3F4h	Floppy Cntrl Status	8bit	RO	First Floppy.
3F5h	Floppy Data	8bit	Yes	First Floppy.
3F6h	No Specific Usage	8bit	---
3F7h	Floppy Conf Reg	8bit	Shw$	First Floppy.
				MSR bit enables/disables into I/O
				3FFh space. (UART1 MSR
3F8h-3FFh	UART/IR - COM1	8bit	---	51400014h[18:16], UART2 MSR
				51400014h[22:20]). Defaults to
				LPC.
480h	No Specific Usage	8bit	WO	Write LPC and DMA. Read only DMA.
481h	DMA Channel 2 High Page	8bit	Rec	Upper addr bits [31:24]. Write LPC and DMA.
				Read only DMA.
482h	DMA Channel 3 High Page
483h	DMA Channel 1 High Page
484h-486h	No Specific Usage	8bit	WO	Write LPC and DMA. Read only DMA.
487h	DMA Channel 0 High Page	8bit	Rec	Upper addr bits [31:24]. Write LPC and DMA.
				Read only DMA.
489h	DMA Channel 6 High Page	8bit	Rec	Upper addr bits [31:24]. Write LPC and DMA.
				Read only DMA.
48Ah	DMA Channel 7 High Page
48Bh	DMA Channel 5 High Page
48Ch-48Eh	No Specific Usage	8bit	WO	Write LPC and DMA. Read only DMA.
48Fh	DMA Channel 4 High Page	8bit	Rec	Upper addr bits [31:24]. Write LPC and DMA.
				Read only DMA.
490h-4CFh	No Specific Usage	---	---
4D0h	PIC Level/Edge	8bit	Yes	IRQ0-IRQ 7.
4D1h	PIC Level/Edge	8bit	Yes	IRQ8-IRQ15.
4D2h-4FFh	No Specific Usage	---	---

Note 1: The Diverse Device Snoops writes to this port and maintains the MSB as NMI enabled. When low, NMI is enabled. When high, NMI is disabled. This bit defaults high. Reads of this port return bits [6:0] from the on-chip or off-chip target, while Bit 7 is returned from the “maintained” value.

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