AM186ES-40VCW datasheet(39/102 Pages) AMD

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Am186/188ES and Am186/188ESLV Microcontrollers

P R E L IMINA R Y

BUS OPERATION

The industry-standard 80C186 and 80C188 microcon-

trollers use a multiplexed address and data (AD) bus.

The address is present on the AD bus only during the

t1 clock phase. The Am186ES and Am188ES micro-

controllers continue to provide the multiplexed AD bus

and, in addition, provide a nonmultiplexed address (A)

bus. The A bus provides an address to the system for

the complete bus cycle (t1–t4).

For systems where power consumption is a concern, it

is possible to disable the address from being driven on

the AD bus on the Am186ES microcontroller and on the

AD and AO buses on the Am188ES microcontroller

during the normal address portion of the bus cycle for

accesses to UCS and/or LCS address spaces. In this

mode, the affected bus is placed in a high-impedance

state during the address portion of the bus cycle. This

feature is enabled through the DA bits in the UMCS and

LMCS registers. When address disable is in effect, the

number of signals that assert on the bus during all nor-

mal bus cycles to the associated address space is re-

duced, decreasing power consumption and reducing

processor switching noise. On the Am188ES micro-

controller, the address is driven on A015–A08 during

the data portion of the bus cycle regardless of the set-

ting of the DA bits.

If the ADEN pin is pulled Low during processor reset,

the value of the DA bits in the UMCS and LMCS regis-

ters is ignored and the address is driven on the AD bus

for all accesses, thus preserving the industry-standard

80C186 and 80C188 microcontrollers’ multiplexed ad-

dress bus and providing support for existing emulation

tools.

The following diagrams show the Am186ES and

AM188ES microcontroller bus cycles when the ad-

dress bus disable feature is in effect:

n Figure 4 shows the affected signals during a normal

read or write operation for an Am186ES microcon-

troller. The address and data are multiplexed onto

the AD bus.

n Figure 5 shows an Am186ES microcontroller bus

cycle when address bus disable is in effect. This re-

sults in the AD bus operating in a nonmultiplexed

address/data mode. The A bus has the address

during a read or write operation.

n Figure 6 shows the affected signals during a normal

read or write operation for an Am188ES microcon-

troller. The multiplexed address/data mode is com-

p a tib l e

wi th

t he

8 0 C1 86

an d

80C 188

microcontrollers and might be used to take advan-

tage of existing logic or peripherals.

n Figure 7 shows an Am188ES microcontroller bus

cycle when address bus disable is in effect. The ad-

dress and data is not multiplexed. The AD7–AD0

signals have only data on the bus, while the AO bus

has the address during a read or write operation.

Figure 4.

Am186ES Microcontroller Address Bus—Normal Read and Write Operation

CLKOUTA

AD15–AD0

(Read)

Data

AD15–AD0

(Write)

LCS or UCS

Address

Data

Address

Phase

Data

Phase

A19–A0

Address

MCSx, PCSx

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