Datasheet

Philips Semiconductors Product specification

8XC54/58

8XC51FA/FB/FC/80C51FA

8XC51RA+/RB+/RC+/RD+/80C51RA+

80C51 8-bit microcontroller family

8K–64K/256–1K OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Aug 07

PIN DESCRIPTIONS (Continued)

PIN NUMBER

MNEMONIC DIP LCC QFP TYPE NAME AND FUNCTION

PSEN 29 32 26 O Program Store 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/V

31 35 29 I External Access Enable/Programming Supply Voltage: EA must be externally held low

to enable the device to fetch code from external program memory locations starting with

0000H. If EA

is held high, the device executes from internal program memory unless the

program counter contains an address greater than 8k Devices (IFFFH), 16k Devices

(3FFFH) or 32k Devices (7FFFH). Since the RD+ has 64k Internal Memory, the RD+ will

execute only from internal memory when EA

is held high. This pin also receives the 12.75 V

programming supply voltage (V

) during EPROM programming. If security bit 1 is

programmed, EA

will be internally latched on Reset.

XTAL1 19 21 15 I Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator

circuits.

XTAL2 18 20 14 O Crystal 2: Output from the inverting oscillator amplifier.

NOTE:

To avoid “latch-up” effect at power-on, the voltage on any pin at any time must not be higher than V

+ 0.5 V or V

– 0.5 V, respectively.