Rainbow-electronics AT89C2051 Bedienungsanleitung PDF herunterladen (Seite 1)

5-47

Using the AT89C2051 Microcontroller

as a Virtual Machine

It is often cited that what differentiates an

embedded microcontroller from other

general purpose computing devices is its

integration into a larger electrical or elec-

tro-mechanical system. While this is

generally true, the fact remains that pro-

cessors of widely differing capability and

architecture are employed in this regard.

Unfortunately, this broad explanation

defines nothing; we are still left to con-

tend with everything from full-blown

embedded PCs to the smallest self-con-

tained single-chip microcontrollers.

Within this expansive realm, conven-

tional wisdom may lead to the conclu-

sion that the smallest microcontrollers

are only appropriate for driving small-

scale applications with very limited pro-

cessing requirements. While this is

unquestionably the case in many

instances, a class of applications exists

that mandates a relatively high level of

program complexity within severely con-

strained space limitations. Faced with

such a seeming paradox, engineers

often feel they have no choice but to

adopt a less than optimal design strat-

egy using a larger microcontroller than

originally intended.

The problem, of course, is one of limited

resources. Functional complexity implies

a non-trivial program, and the greater

the functional complexity the larger the

program. Even as the capability of small

single-chip microcontrollers continu-

ously inches upwards, application

requirements seem to grow at a com-

mensurate rate. Trying to hit such a

moving target is difficult at best.

The economy of using a microcontroller

with just enough processing power for a

given application is a potent incentive to

find just the right fit. Of course, this only

works when the system requirements

are thoroughly understood and clearly

defined. Since such a design normally

has little reserve capacity, it is usually

hard pressed to handle features beyond

those originally specified. Should addi-

tional capabilities eventually become a

necessity, the result could be a system

that runs out of steam and an engineer

that runs out of options. Such are the

perils of designing on the edge.

Atmel’s AT89C2051 offers capabilities

that far exceed those of competing

devices of similar size. This opens up

potential design opportunities that were

simply unattainable with previously avail-

able parts. Housed in a 20-pin package,

Atmel’s miniature microcontroller retains

all the major features of the 8051 archi-

tecture. Furthermore, the AT89C2051

includes all of the 8051’s “special” pins

including the external interrupts, UART

transmit and receive lines, and the exter-

nal timer controls. Even though the

AT89C2051 significantly ups the pro-

cessing ante, it would seem that there

are limits to what you can accomplish

with any single-chip microcontroller.

This dilemma is nothing new. The tradi-

tional way of dealing with such limita-

tions has been to operate the microcon-

troller in external memory mode. Com-

mon sense would indicate the hopeless-

ness of applying such an approach to

the AT89C2051. After all, the

AT89C2051 is truly a single-chip design

that does not even possess an external

bus structure. It turns out that the situa-

tion is not hopeless at all.

AT89C2051

Flash

Microcontroller

Application

Note

1 2 3 4 5 6 ... 10 11

Inhaltsverzeichnis

Seite 1 - Application

5-47Using the AT89C2051 Microcontroller as a Virtual MachineIt is often cited that what differentiates anembedded microcontroller from othergeneral pu

Seite 2

Microcontroller5-56Table 4. Compare ModifiersNotes: 1. These instructions must immediately follow a CMP instruction.2. NOT instruction is used to imp

Seite 3

Microcontroller5-57Table 7. Miscellaneous InstructionsNote: 1. ALT obtains the remainder after DIV and obtains the high word after a multiply. This i

Seite 4

Microcontroller5-48Processor SimulationThe concept of microprocessor simulation is widely usedand well understood. Simulation is often used for develo

Seite 5

Microcontroller5-49The greatest overhead burden that I2C imposes involvesthe transfer of addressing information. For every randomread or write, a 16-b

Seite 6

Microcontroller5-50The bulk of the virtual instruction set is presented in Table3. These instructions include memory access instructions,arithmetic in

Seite 7

Microcontroller5-51Figure 1. 8K Virtual Machine10 Fµ+510K1N914RSTAT89C2051XTAL2415236XTAL1RXD/P3.0TXD/P3.17891110INT0/P3.2INT1/P3.3T0/P3.4T1/P3.5P3.7

Seite 8

Microcontroller5-52Virtual Machine I/OThe Virtual Machine handles physical I/O (as well as virtualI/O) through the use of input/output instructions. I

Seite 9

Microcontroller5-53Pint Sized ComputerAlthough tiny by any scale of measure, the Virtual machinebehaves the way you would expect any self respecting p

Seite 10

Microcontroller5-54Appendix A — Virtual Machine ArchitectureTable 1. Fundamental Resource SetTable 2. General Addressing ModesNotes: 1. Addressing m

Seite 11

Microcontroller5-55Table 3. Memory Addressing InstructionsNotes: 1. ACC always contains 16 valid bits. All operations are performed in 16-bit precisi

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