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AT89S52 Datasheet(PDF) 6 Page - ATMEL Corporation |
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AT89S52 Datasheet(HTML) 6 Page - ATMEL Corporation |
6 / 38 page ![]() 6 1919D–MICRO–6/08 AT89S52 4.9 PSEN Program Store Enable (PSEN) is the read strobe to external program memory. When the AT89S52 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to exter- nal data memory. 4.10 EA/VPP External Access Enable. EA must be strapped to GND in order 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, EA will be internally latched on reset. EA should be strapped to V CC for internal program executions. This pin also receives the 12-volt programming enable voltage (V PP) during Flash programming. 4.11 XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit. 4.12 XTAL2 Output from the inverting oscillator amplifier. 5. Special Function Registers A map of the on-chip memory area called the Special Function Register (SFR) space is shown in Table 5-1. Note that not all of the addresses are occupied, and unoccupied addresses may not be imple- mented on the chip. Read accesses to these addresses will in general return random data, and write accesses will have an indeterminate effect. User 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 in registers T2CON (shown in Table 5- 2) and T2MOD (shown in Table 10-2) 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 interrupt sources in the IP register. |
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Similar Description - AT89S52_08 |
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