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AT89C52-24PC Datasheet(PDF) 4 Page - ATMEL Corporation |
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AT89C52-24PC Datasheet(HTML) 4 Page - ATMEL Corporation |
4 / 24 page AT89C52 4 timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external data memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only dur- ing 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. PSEN Program Store Enable is the read strobe to external pro- gram memory. When the AT89C52 is executing code from external pro- gram memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory. EA/VPP External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external pro- gram memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to V CC f o r int e r nal pr ogr am executions. This pin also receives the 12-volt programming enable volt- age (V PP ) du r i ng F l as h pr o g r a mm ing whe n 1 2 - v ol t 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. Table 1. AT89C52 SFR Map and Reset Values 0F8H 0FFH 0F0H B 00000000 0F7H 0E8H 0EFH 0E0H ACC 00000000 0E7H 0D8H 0DFH 0D0H PSW 00000000 0D7H 0C8H T2CON 00000000 T2MOD XXXXXX00 RCAP2L 00000000 RCAP2H 00000000 TL2 00000000 TH2 00000000 0CFH 0C0H 0C7H 0B8H IP XX000000 0BFH 0B0H P3 11111111 0B7H 0A8H IE 0X000000 0AFH 0A0H P2 11111111 0A7H 98H SCON 00000000 SBUF XXXXXXXX 9FH 90H P1 11111111 97H 88H TCON 00000000 TMOD 00000000 TL0 00000000 TL1 00000000 TH0 00000000 TH1 00000000 8FH 80H P0 11111111 SP 00000111 DPL 00000000 DPH 00000000 PCON 0XXX0000 87H |
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