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1、AT89S52The AT89S52 is a low-power, high-performance CMOS 8-bit microcomputer with 8K bytes of Flash programmable and erasable read only memory (PEROM). The device is manufactured using Atmels high-density nonvolatile memory technology and is compatible with the industry-standard 80S51 and 80S52 inst
2、ruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcomputer which provides a highly-flexible and
3、cost-effective solution to many embedded control applications. The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full-duplex serial port, on-chip oscillator, and clock
4、 circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-do
5、wn mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next hardware reset.VCC: Supply voltage.GND: Ground.Port 0: Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to por
6、t 0 pins, the pins can be used as high-impedance inputs. Port 0 can also be configured to be the multiplexed low-order address/data bus during accesses to external pro-gram and data memory. In this mode, P0 has internal pullups. Port 0 also receives the code bytes during Flash programming and output
7、s the code bytes during program verification. External pullups are required during program verification.Port 1: Port 1 is an 8-bit bi-directional I/O port with internal pullups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the
8、 internal pullups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pullups. In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2 trigger in
9、put (P1.1/T2EX), respectively, as shown in the following table. Port 1 also receives the low-order address bytes during Flash programming and verification.Port 2: Port 2 is an 8-bit bi-directional I/O port with internal pullups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are
10、written to Port 2 pins, they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pullups. Port 2 emits the high-order address byte during fetches from external program memory
11、and during accesses to external data memory that use 16-bit addresses (MOVX DPTR). In this application, Port 2 uses strong internal pullups when emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX RI), Port 2 emits the contents of the P2 Special Function Register. Por
12、t 2 also receives the high-order address bits and some control signals during Flash programming and verification.Port 3: Port 3 is an 8-bit bi-directional I/O port with internal pullups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled hi
13、gh by the internal pullups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pullups. Port 3 also serves the functions of various special features of the AT89C51, as shown in the following table. Port 3 also receives some
14、control signals for Flash programming and verification.RST: Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.ALE/: Address Latch Enable is an output pulse for latching thelow byte of the address during accesses to external memory. This pin is a
15、lso the program pulse input (PROG) during Flash programming. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external data memory. If de
16、sired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.:Program Store E
17、nable is the read strobe to external pro-gram memory. When the AT89S52 is executing code from external pro-gram memory, is activated twice each machine cycle, except that two activations are skipped during each access to external data memory./VPP：External Access Enable. must be strapped to GND in or
18、der to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, will be internally latched on reset. should be strapped to Vcc for internal program executions. This pin also receives the 12-volt programming
19、 enable voltage (Vpp) during Flash programming when 12-volt programming is selected.XTAL1：Input to the inverting oscillator amplifier and input to the internal clock operating circuit.XTAL2：Output from the inverting oscillator amplifier.Special Function Registers：A map of the on-chip memory area cal
20、led the Special Function Register (SFR) space is shown in Table 1.Note that not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip. Read accesses to these addresses will in general return random data, and write accesses will have an indeterminate effect. U
21、ser software should not write 1s to these unlisted locations, since they may be used in future products to invoke new features. In that case, the reset or inactive values of the new bits will always be 0. Timer 2 Registers Control and status bits are contained inregisters T2CON (shown in Table 2) an
22、d T2MOD (shown in Table 4) for Timer 2. The register pair (RCAP2H, RCAP2L)are the Capture/Reload registers for Timer 2 in 16-bit capture mode or 16-bit auto-reload mode. Interrupt Registers The individual interrupt enable bits are in the IE register. Two priorities can be set for each of the six int
23、errupt sources in the IP register.Data Memory：The AT89S52 implements 256 bytes of on-chip RAM. The upper 128 bytes occupy a parallel address space to the Special Function Registers. That means the upper 128 bytes have the same addresses as the SFR space but are physically separate from SFR space. Wh
24、en an instruction accesses an internal location above address 7FH, the address mode used in the instruction specifies whether the CPU accesses the upper 128 bytes of RAM or the SFR space. Instructions that use direct addressing access SFR space. For example, the following direct addressing instructi
25、on accesses the SFR at location 0A0H (which is P2). MOV 0A0H, #dataInstructions that use indirect addressing access the upper128 bytes of RAM. For example, the following indirect addressing instruction, where R0 contains 0A0H, accesses the data byte at address 0A0H, rather than P2 (whose address is
26、0A0H).MOV R0, #dataNote that stack operations are examples of indirect addressing, so the upper 128 bytes of data RAM are available as stack space.InfraredInfrared(IR)lightiselectromagneticradiationwithawavelengthlongerthanthatofvisiblelight,measuredfromthenominaledgeofvisibleredlightat0.74microm-et
27、res(m),andextendingconventionallyto300m.Thesewavelengthscorrespondtoafrequencyrangeofapproximately1to400THz,andincludemostofthethermalradiationemittedbyobjectsnearroomtemperature.Microscopically,IRlightistypicallyemittedorabsorbedbymoleculeswhentheychangetheirrotational-vibrationalmovements.Infrared
28、lightisusedinindustrial,scientific,andmedicalapplications.Night-visiondevicesusinginfraredilluminationallowpeopleoranimalstobeobservedwithouttheobserverbeingdetected.Inastronomy,imagingatinfraredwavelengthsallowsobservationofobjectsobscuredbyinterstellardust.Infraredimagingcamerasareusedtodetectheat
29、lossininsulatedsystems,observechangingbloodflowintheskin,andoverheatingofelectricalapparatus. MuchoftheenergyfromtheSunarrivesonEarthintheformofinfraredradiation.Sunlightatzenithprovidesanirradianceofjustover1kilowattpersquaremeteratsealevel.Ofthisenergy,527wattsisinfraredradiation,445wattsisvisible
30、light,and32wattsisultravioletradiation.ThebalancebetweenabsorbedandemittedinfraredradiationhasacriticaleffectontheEarthsclimate.Objectsgenerallyemitinfraredradiationacrossaspectrumofwavelengths,butsometimesonlyalimitedregionofthespectrumisofinterestbecausesensorsusuallycollectradiationonlywithinaspe
31、cificbandwidth.Therefore,theinfraredbandisoftensubdividedintosmallersections. MuchoftheenergyfromtheSunarrivesonEarthintheformofinfraredradiation.Sunlightatzenithprovidesanirradianceofjustover1kilowattpersquaremeteratsealevel.Ofthisenergy,527wattsisinfraredradiation,445wattsisvisiblelight,and32watts
32、isultravioletradiation.ThebalancebetweenabsorbedandemittedinfraredradiationhasacriticaleffectontheEarthsclimate.Objectsgenerallyemitinfraredradiationacrossaspectrumofwavelengths,butsometimesonlyalimitedregionofthespectrumisofinterestbecausesensorsusuallycollectradiationonlywithinaspecificbandwidth.T
33、herefore,theinfraredbandisoftensubdividedintosmallersections. Heat/HeatingInfraredradiationispopularlyknownasheatradiation,butlightandelectromagneticwavesofanyfrequencywillheatsurfacesthatabsorbthem.Infrared lightfromtheSunonlyaccountsfor49%oftheheatingoftheEarth,withtherestbeingcausedbyvisiblelight
34、thatisabsorbedthenre-radiatedatlonger wave lengths.Visiblelightorultraviolet-emittinglaserscancharpaperandincandescentlyhotobjectsemitvisibleradiation.Objectsatroomtemperaturewillemitradiationmostlyconcentratedinthe8to25mband,butthisisnotdistinctfromtheemissionofvisiblelightbyincandescentobjectsandu
35、ltravioletbyevenhotterobjects(seeblackbodyandWiensdisplacementlaw).Heatisenergyintransientformthatflowsduetotemperaturedifference.Unlikeheattransmittedbythermalconductionorthermalconvection,radiationcanpropagatethroughavacuum.Theconceptofemissivityisimportantinunderstandingtheinfraredemissionsofobje
36、cts.Thisisapropertyofasurfacewhichdescribeshowitsthermalemissionsdeviatefromtheidealofablackbody.Tofurtherexplain,twoobjectsatthesamephysicaltemperaturewillnotappearthesametemperatureinaninfraredimageiftheyhavedifferingemissivities.ThermographyInfraredradiationcanbeusedtoremotelydeterminethetemperat
37、ureofobjects(iftheemissivityisknown).Thisistermedthermography,orinthecaseofveryhotobjectsintheNIRorvisibleitistermedpyrometry.Thermography(thermalimaging)ismainlyusedinmilitaryandindustrialapplicationsbutthetechnologyisreachingthepublicmarketintheformofinfraredcamerasoncarsduetothemassivelyreducedpr
38、oductioncosts.Thermographic. camerasdetectradiationintheinfraredrangeoftheelectromagneticspectrum(roughly90014,000nanometersor0.914m)andproduceimagesofthatradiation.Sinceinfraredradiationisemittedbyallobjectsbasedontheirtemperatures,accordingtotheblackbodyradiationlaw,thermographymakesitpossibletose
39、eonesenvironmentwithorwithoutvisibleillumination.Theamountofradiationemittedbyanobjectincreaseswithtemperature,thereforethermographyallowsonetoseevariationsintemperature(hencethename). Infraredradiationcanbeusedasadeliberateheatingsource.Forexampleitisusedininfraredsaunastoheattheoccupants,andalsoto
40、removeicefromthewingsofaircraft(de-icing).FIRisalsogainingpopularityasasafeheattherapymethodofnaturalhealthcare&physiotherapy.Infraredcanbeusedincookingandheatingfoodasitpredominantlyheatstheopaque,absorbentobjects,ratherthantheairaroundthem.Infraredheatingisalsobecomingmorepopularinindustrialmanufa
41、cturingprocesses,e.g.curingofcoatings,formingofplastics,annealing,plasticwelding,printdrying.Intheseapplications,infraredheatersreplaceconvectionovensandcontactheating.Efficiencyisachievedbymatchingthewavelengthoftheinfraredheatertotheabsorptioncharacteristicsofthematerial.ClimatologyInthefieldofcli
42、matology,atmosphericinfraredradiationismonitoredtodetecttrendsintheenergyexchangebetweentheearthandtheatmosphere.ThesetrendsprovideinformationonlongtermchangesintheEarthsclimate.Itisoneoftheprimaryparametersstudiedinresearchintoglobalwarmingtogetherwithsolarradiation.Apyrgeometerisutilizedinthisfiel
43、dofresearchtoperformcontinuousoutdoormeasurements.Thisisabroadbandinfraredradiometerwithsensitivityforinfraredradiationbetweenapproximately4.5mand50m.NightvisionInfraredisusedinnightvisionequipmentwhenthereisinsufficientvisiblelighttosee.Nightvisiondevicesoperatethroughaprocessinvolvingtheconversion
44、ofambientlightphotonsintoelectronswhicharethenamplifiedbyachemicalandelectricalprocessandthenconvertedbackintovisiblelight.Infraredlightsourcescanbeusedtoaugmenttheavailableambientlightforconversionbynightvisiondevices,increasingin-the-darkvisibilitywithoutactuallyusingavisiblelightsource.Theuseofin
45、fraredlightandnightvisiondevicesshouldnotbeconfusedwith thermalimagingwhichcreatesimagesbasedondifferencesinsurfacetemperaturebydetectinginfraredradiation(heat)thatemanatesfromobjectsandtheirsurroundingenvironment. AstronomyAstronomersobserveobjectsintheinfraredportionoftheelectromagneticspectrumusingopticalcomponents,includingmirrors,lensesandsolidstatedigitaldetectors.Forthisreasonitisclassifiedaspartofopticalastronomy.Toformanimage,thecomponentsofaninfraredtelescopeneedtobecarefullyshieldedfromheatsources,andthedetectorsarechilledusingliquidhelium.ThesensitivityofEarth-basedinfrare
