Philips Semiconductors
Product specification
80C51 8-bit microcontroller family
8K–64K/256–1K OTP/ROM/ROMless, low voltage (2.7V–5.5V),
low power, high speed (33 MHz)
8XC54/58
8XC51FA/FB/FC/80C51FA
8XC51RA+/RB+/RC+/RD+/80C51RA+
PIN DESCRIPTIONS
(Continued)
PIN NUMBER
MNEMONIC
PSEN
DIP
29
LCC
32
QFP
26
TYPE
O
NAME AND FUNCTION
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.
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
PP
) during EPROM programming. If security bit 1 is
programmed, EA will be internally latched on Reset.
Crystal 1:
Input to the inverting oscillator amplifier and input to the internal clock generator
circuits.
Crystal 2:
Output from the inverting oscillator amplifier.
EA/V
PP
31
35
29
I
XTAL1
XTAL2
19
18
21
20
15
14
I
O
NOTE:
To avoid “latch-up” effect at power-on, the voltage on any pin at any time must not be higher than V
CC
+ 0.5 V or V
SS
– 0.5 V, respectively.
2000 Aug 07
6
PHILIPS [ NXP SEMICONDUCTORS ]
