【文章內(nèi)容簡介】 itates not only a welldefined process but also a proper environment and tools to facilitate and execute the mission successfullyIntel Chandler Platform Engineering group provides post silicon system validation SV of various microcontrollers and processors The system validation process can be broken into three major partsThe type of the device and its application requirements determine which types of testing are performed on the device 12 The AT89C51 provides the following standard features 4Kbytes of Flash 128 bytes of RAM 32 IO lines two 16bittimercounters a five vector twolevel interrupt architecturea full duple ser ial port onchip oscillator and clock circuitryIn addition the AT89C51 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 timercountersserial port and interrupt sys tem to continue functioning The Powerdown Mode saves the RAM contents but freezes the oscil – lator disabling all other chip functions until the next hardware reset Figure 121Block Diagram 13Pin Description VCC Supply voltage GND Ground Port 0Port 0 is an 8bit opendrain bidirectional IO port As an output port each pin cansink eight TTL inputs When 1s are written to port 0 pins the pins can be used as highimpedance inputsPort 0 may also be configured to be the multiplexed loworder addressdata busduring accesses to external program and data memory In this mode P0 has internalpullupsPort 0 also receives the code bytes during Flash programmingand outputs the codebytes during program verification External pullups are required during programverification Port 1Port 1 is an 8bit bidirectional IO port with internal pullupsThe Port 1 output buffers can sinkso urce four TTL inputsWhen 1s are written to Port 1 pins they are pulled high by the 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 pullupsPort 1 also receives the loworder address bytes during Flash programming and verification Port 2Port 2 is an 8bit bidirectional IO port with internal pullupsThe Port 2 outputbuffers can sinksource four TTL inputsWhen 1s are written to Port 2 pins they arepulled 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 highorder address byte during fetches from external program memory and during accesses to Port 2 pins that are externally being pulled low will source current IIL because of the internal pullupsPort 2 emits the highorder address byte during fetches from external program memory and during accesses to external data memory that use 16bit addresses MOVXDPTR In this application it uses strong internal pullups when emitting 1s During accesses to external data memory that use 8bit addresses MOVX RI Port 2 emits the contents of the P2 Special Function RegisterPort 2 also receives the highorder address bits and some control signals durin Flash programming and verification Port 3Port 3 is an 8bit bidirectional IO port with internal pullupsThe Port 3 outputbuffers can sinksou rce four TTL inputsWhen 1s are written to Port 3 pins they are pulled high by the internal pullups and can be used as inputs As inputsPort 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 featuresof the AT89C51 as listed below RSTReset input A high on this pin for two machine cycles while the oscillator is running resets the device ALEPROGAddress Latch Enable output pulse for latching the low byte of the address duringaccesses to external memoryThis pin is also the program pulse input PROG during Flash programmingIn normal operation ALE is emitted at a constant rate of 16 the oscillator frequencyand may be used for external timing or clocking purposes Note however that one ALEpulse is skipped duri ng each access to external DataMemoryIf desired ALE operationcan be disabled by setting bit 0 of SFR location 8EH With the bit set ALE is active onlyduring a MOVX or MOVC instruction Otherwise the pin is weakly pulled high Settingthe ALEdisable bit has no effect if the microcontroller is in external execution mode PSENProgram Store Enable is the read strobe to external program memory When theAT89C51