Rainbow-electronics T89C51IC2 Manual de usuario descargar pdf (Pagina 8)

T89C51IC2

Rev. C – 3-Dec-01

RST 10 4 I/O

Reset: A high on this pin for two machine cycles while the oscillator is running, resets

the device. An internal diffused resistor to V

permits a power-on reset using only an

external capacitor to V

. This pin is an output when the hardware watchdog forces a

system reset.

ALE/PROG

33 27 O (I) Address Latch Enable/Program Pulse: Output pulse for latching the low byte of the

address during an access to external memory. In normal operation, ALE is emitted at a

constant rate of 1/6 (1/3 in X2 mode) the oscillator frequency, and can be used for

external timing or clocking. Note that one ALE pulse is skipped during each access to

external data memory. This pin is also the program pulse input (PROG

) during Flash

programming. ALE can be disabled by setting SFR’s AUXR.0 bit. With this bit set, ALE

will be inactive during internal fetches.

PSEN 32 26 O Program Strobe ENable: The read strobe to external program memory. When

executing code from the external program memory, PSEN

is activated twice each

machine cycle, except that two PSEN

activations are skipped during each access to

external data memory. PSEN

is not activated during fetches from internal program

memory.

EA 35 29 I External Access Enable: EA

must be externally held low to enable the device to fetch

code from external program memory locations 0000H to FFFFH (RD). If security level 1

is programmed, EA

will be internally latched on Reset.

Mnemonic

Pin Number

Type

Name and FunctionPLCC44 VQFP44 1.4

1 2 3 4 5 6 7 8 9 10

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Rainbow-electronics T89C51IC2 Manual de usuario Pagina 8