AT89S52-24AC Просмотр технического описания (PDF) - Atmel Corporation
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AT89S52-24AC Datasheet PDF : 39 Pages
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4.9 PSEN
4.10 EA/VPP
4.11 XTAL1
4.12 XTAL2
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.
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 VCC for internal program executions.
This pin also receives the 12-volt programming enable voltage (VPP) during Flash programming.
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
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.
6 AT89S52
1919C–MICRO–3/05
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