AMD-K6-2ESLASH233AMZ datasheet(104/332 Pages) AMD

104 / 332 page

Signal Descriptions

Chapter 5

AMD-K6™-2E Processor Data Sheet

22529B/0—January 2000

Preliminary Information

5.2

A20M# (Address Bit 20 Mask)

Pin Attribute

Input

Pin Location

AK-08

Summary

A20M# is used to simulate the behavior of the 8086 when

running in real mode. The assertion of A20M # causes the

processor to force bit 20 of the physical address to 0 prior to

accessing the cache or driving out a memory bus cycle. The

clearing of address bit 20 maps addresses that wrap above

1 Mbyte to addresses below 1 Mbyte.

Sampled

The processor samples A20M # as a level-sensitive input on

every clock edge. The system logic can drive the signal either

sync hr o n ousl y or async h r o nousl y. I f i t is ass e r t ed

asynchronously, it must be asserted for a minimum pulse width

of two clocks.

The following list explains the effects of the processor sampling

A20M# asserted under various conditions:

Inquire cycles and writeback cycles are not affected by the

state of A20M#.

The assertion of A20M# in system management mode

(SMM) is ignored.

When A20M# is sampled asserted in protected mode, it

causes unpredictable processor operation. A20M# is only

defined in real mode.

To ensure that A20M# is recognized before the first ADS#

occurs following the negation of RESET, A20M# must be

sampled asserted on the same clock edge that RESET is

sampled negated or on one of the two subsequent clock

edges.

To ensure A20M# is recognized before the execution of an

instruction, a serializing instruction must be executed

between the instruction that asserts A20M# and the

targeted instruction.

AMD-K6-2E/233AMZ Datasheet(PDF) 104 Page - Advanced Micro Devices

AMD-K6-2E/233AMZ Datasheet(HTML) 104 Page - Advanced Micro Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL