P89V51RB2BBC datasheet(9/77 Pages) PHILIPS

9 / 77 page

Philips Semiconductors

P89V51RB2/RC2/RD2

8-bit microcontrollers with 80C51 core

Product data

Rev. 03 — 02 December 2004

9 of 77

9397 750 14341

[1]

ALE loading issue: When ALE pin experiences higher loading (>30 pF) during the reset, the microcontroller may accidentally enter into

modes other than normal working mode. The solution is to add a pull-up resistor of 3 k

Ω to 50 kΩ to V

DD, e.g., for ALE pin.

[2]

For 6-clock mode, ALE is emitted at 1

⁄

3 of crystal frequency.

External Access Enable: EA must be connected to VSS

in order to enable the device to fetch code from the

external program memory. EA must be strapped to VDD

for internal program execution. However, Security lock

level 4 will disable EA, and program execution is only

possible from internal program memory. The EA pin can

tolerate a high voltage of 12 V.

ALE/

PROG

I/O

Address Latch Enable: ALE is the output signal for

latching the low byte of the address during an access to

external memory. This pin is also the programming

pulse input (PROG) for ﬂash programming. Normally the

ALE[1] is emitted at a constant rate of 1

⁄

6 the crystal

frequency[2] and can be used for external timing and

clocking. One ALE pulse is skipped during each access

to external data memory. However, if AO is set to ‘1’,

ALE is disabled.

6, 17, 28,

1, 12, 23,

I/O

No Connect

XTAL1

Crystal 1: Input to the inverting oscillator ampliﬁer and

input to the internal clock generator circuits.

XTAL2

Crystal 2: Output from the inverting oscillator ampliﬁer.

VDD

Power supply

VSS

Ground

Table 3:

P89V51RB2/RC2/RD2 pin description…continued

Symbol

Type

Description

DIP40

TQFP44

PLCC44

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