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The I/O address space of ISA is 16 bits; correct this, but add a note 

explaining why it is often treated as only having 10 bits of I/O
address space.
This commit is contained in:
nathanw 2001-07-05 18:01:15 +00:00
parent fd1fd6bb0f
commit e927c2a3b8
1 changed files with 6 additions and 4 deletions
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10
share/man/man9/isa.9
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@ -1,4 +1,4 @@
.\" $NetBSD: isa.9,v 1.1 2001/07/01 04:11:14 gmcgarry Exp $
.\" $NetBSD: isa.9,v 1.2 2001/07/05 18:01:15 nathanw Exp $
.\"
.\" Copyright (c) 2001 The NetBSD Foundation, Inc.
.\" All rights reserved.
@ -127,9 +127,11 @@ widespread acceptance of the bus as a defacto standard has seen it
appear on systems without Intel processors.
.Pp
The ISA bus has a 16-bit data bus, a 24-bit memory address bus, a
10-bit I/O address bus and operates at 8MHz. It provides 15 interrupt
lines and 8 DMA channels supporting DMA transfers of 64KB or 128KB
transfers depending on the width of the channel being used.
16-bit I/O address bus, and operates at 8MHz. It provides 15
interrupt lines and 8 DMA channels supporting DMA transfers of 64KB or
128KB transfers depending on the width of the channel being
used. Historically, some devices only decoded the 10 lowest bits of
the I/O address bus, preventing use of the full 16-bit address space.
.Pp
On newer machines, the ISA bus is no longer connected directly to the
host bus, and is usually connected via a PCI-ISA bridge. Either way,