Signal Descriptions
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18524C/0—Nov1996
AMD-K5 Processor Technical Reference Manual
address limit required in Real mode. (The physical address
000F_FFF0h is sometimes written in the selector:offset format
as F000:FFF0.) This reset address behavior of the x86 architec-
ture is due to the special way in which segment translation is
performed on reset. Normally, a Real-mode 16-bit segment
selector is shifted left 4 bits (one hex digit) to form the seg-
ment base, and then added to the 16-bit offset. Thus,
F000:FFF0 in the selector:offset format becomes a segment base
of F0000h added to an offset of FFF0h, yielding the physical
address 000F_FFF0h. When RESET is asserted, however, the
left shift is not done and the high 16 address bits are all set to
1, yielding the physical address FFFF_FFF0h. Thereafter,
address translation only begins to work in the normal Real-
mode manner when the first far jump is executed. This jump
loads the code segment register with a 16-bit segment selector.
This code segment load causes the address translation mecha-
nism to begin working normally. The system logic address
decoder must make this behavior transparent to software by
aliasing the physical address FFFF_FFF0h to the physical
address 000F_FFF0h.
The processor recognizes AHOLD, BOFF, and HOLD while
RESET is asserted, but these signals will not intervene in the
initialization process except that they will prevent the first
code fetch (jump to BIOS) after the registers are initialized.
While RESET is asserted, the processor recognizes or drives
only BF (BF1–BF0), FLUSH, FRCMC, the hold signals
(AHOLD, BOFF, HOLD, and HLDA), INIT, and R/S.
Unlike the Pentium processor, the AMD-K5 processor does not
recognize RESET in the Hardware Debug Tool (HDT) mode.
System hardware or software must exit the HDT (by driving R/
S High) before asserting RESET.
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...