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8XL52 Scheda tecnica(PDF) 5 Page - Intel Corporation |
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8XL52 Scheda tecnica(HTML) 5 Page - Intel Corporation |
5 / 20 page 8XL525458 ALE Address Latch Enable output pulse for latching the low byte of the address during accesses to ex- ternal memory This pin (ALEPROG) is also the program pulse input during OTP ROM programming for the 87L5X In normal operation ALE is emitted at a constant rate of the oscillator frequency and may be used for external timing or clocking purposes Note how- ever that one ALE pulse is skipped during each ac- cess to external Data Memory If desired ALE operation can be disabled by setting bit 0 of SFR location 8EH With this bit set the pin is weakly pulled high However the ALE disable fea- ture will be suspended during a MOVX or MOVC in- struction idle mode power down mode and ICE mode The ALE disable feature will be terminated by reset When the ALE disable feature is suspended or terminated the ALE pin will no longer be pulled up weakly Setting the ALE-disable bit has no affect if the microcontroller is in external execution mode Throughout the remainder of this data sheet ALE will refer to the signal coming out of the ALEPROG pin and the pin will be referred to as the ALEPROG pin PSEN Program Store Enable is the read strobe to external Program Memory When the 8XL5X is executing code from external Program Memory PSEN is activated twice each ma- chine cycle except that two PSEN activations are skipped during each access to external Data Memo- ry EA VPP External Access enable EA must be strapped to VSS in order to enable the device to fetch code from external Program Memory locations 0000H to 0FFFH Note however that if either of the Program Lock bits are programmed EA will be inter- nally latched on reset EA must be strapped to VCC for internal program executions This pin also receives the programming supply volt- age (VPP) during OTP ROM programming XTAL1 Input to the inverting oscillator amplifier XTAL2 Output from the inverting oscillator amplifier OSCILLATOR CHARACTERISTICS XTAL1 and XTAL2 are the input and output respec- tively of a inverting amplifier which can be config- ured for use as an on-chip oscillator as shown in Figure 3 Either a quartz crystal or ceramic resonator may be used More detailed information concerning the use of the on-chip oscillator is available in Appli- cation Note AP-155 ‘‘Oscillators for Microcontrol- lers’’ To drive the device from an external clock source XTAL1 should be driven while XTAL2 floats as shown in Figure 4 There are no requirements on the duty cycle of the external clock signal since the in- put to the internal clocking circuitry is through a di- vide-by-two flip-flop but minimum and maximum high and low times specified on the data sheet must be observed An external oscillator may encounter as much as a 100 pF load at XTAL1 when it starts up This is due to interaction between the amplifier and its feedback capacitance Once the external signal meets the VIL and VIH specifications the capacitance will not ex- ceed 20 pF 272468 – 4 C1 C2 e 30 pF g10 pF for Crystals For Ceramic Resonators contact resonator manufacturer Figure 3 Oscillator Connections 272468 – 5 Figure 4 External Clock Drive Configuration IDLE MODE The user’s software can invoke the Idle Mode When the microcontroller is in this mode power consump- tion is reduced The Special Function Registers and the onboard RAM retain their values during Idle but the processor stops executing instructions Idle Mode will be exited if the chip is reset or if an en- abled interrupt occurs The PCA timercounter can optionally be left running or paused during Idle Mode 5 |
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Descrizione simile - 8XL52 |
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