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BN87C51FB Datasheet(PDF) 5 Page - Intel Corporation |
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BN87C51FB Datasheet(HTML) 5 Page - Intel Corporation |
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5 / 18 page  AUTOMOTIVE 87C51FAFBFCFC-20 Port 2 emits the high-order address byte during fetches from external Program Memory and during accesses to external Data Memory that use 16-bit addresses (MOVX DPTR) In this application it uses strong internal pullups when emitting 1’s Dur- ing accesses to external Data Memory that use 8-bit addresses (MOVX Ri) Port 2 emits the contents of the P2 Special Function Register Some Port 2 pins receive the high-order address bits during EPROM programming and program verifica- tion Port 3 Port 3 is an 8-bit bidirectional IO port with internal pullups The Port 3 output buffers can drive LS TTL inputs Port 3 pins that have 1’s written to them are pulled high by the internal pullups and in that state can be used as inputs As inputs Port 3 pins that are externally pulled low will source current (IIL on the data sheet) because of the pullups Port 3 also serves the functions of various special features of the MCS-51 Family as listed below Port Pin Alternate Function P30 RXD (serial input port) P31 TXD (serial output port) P32 INT0 (external interrupt 0) P33 INT1 (external interrupt 1) P34 T0 (Timer 0 external input) P35 T1 (Timer 1 external input) P36 WR (external data memory write strobe) P37 RD (external data memory read strobe) RST Reset input A high on this pin for two machine cycles while the oscillator is running resets the de- vice The port pins will be driven to their reset condi- tion when a minimum VIH1 is applied whether the oscillator is running or not An internal pulldown re- sistor permits a power-on reset with only a capacitor connected to VCC ALEPROG Address Latch Enable output pulse for latching the low byte of the address during accesses to external memory This pin (ALEPROG) is also the program pulse input during EPROM program- ming for the 87C51FAFBFC 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 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 87C51FAFBFC is executing code from external Program Memory PSEN is activated twice each machine cycle except that two PSEN activa- tions are skipped during each access to external Data Memory 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 0FFFFH Note however that if either of the Program Lock bits are programmed EA will be internally latched on reset EA should be strapped to VCC for internal program executions This pin also receives the programming supply volt- age (VPP) during EPROM 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 an inverting amplifier which can be config- ured for use as an on-chip oscillator as shown in Figure 4 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’’ and in Application Note AP-486 ‘‘Oscillator Design for Microcontrollers’’ 5 |
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