Signal Descriptions
5-95
18524C/0—Nov1996
AMD-K5 Processor Technical Reference Manual
5.2.36
M/IO (Memory or I/O)
Output
Summary
The processor drives M/IO to indicate whether it is accessing
memory or I/O on the bus. The signal is driven at the same time
as the other two cycle definition signals, D/C and W/R. A spe-
cific encoding of D/C, M/IO, and W/R identifies one of several
special bus cycles.
Driven and Floated
M/IO is driven and floated with the same timing as D/C. See the
description of D/C on page 5-53.
Details
The processor accesses I/O when it executes an I/O instruction
(any of the INx or OUTx instructions). The processor accesses
memory when it fetches instructions or executes an instruction
that loads or stores data. Accesses to memory-mapped I/O ports
appear on the bus as memory accesses.
Only data (not code) can be read or written from the I/O
address space; the cycle definition for an I/O code read (D/C =
0, M/IO = 0, W/R = 0) defines an interrupt acknowledge cycle,
and the cycle definition for an I/O code write (D/C = 0, M/IO =
0, W/R = 1) defines a special bus cycle.
The processor specifies all special bus cycles with D/C = 0,
M/IO = 0, and W/R = 1. The cycles are then differentiated by
BE7–BE0 and A31–A3.
Summary of Contents for AMD-K5
Page 1: ...AMD K5 Processor Technical Reference Manual TM...
Page 10: ...x AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 24: ...1 4 Overview AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 54: ...2 30 Internal Architecture AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 116: ...4 26 Performance AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 356: ...6 44 System Design AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 380: ...7 24 Test and Debug AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 396: ...A 16 AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...
Page 406: ...I 10 Index AMD K5 Processor Technical Reference Manual 18524C 0 Nov1996...