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P80C51HFH

Low-voltage single-chip 8-bit microcontrollers

Philips Electronics 

Philips Semiconductors

Low-voltage single-chip 8-bit microcontrollers

Product specification

80CL31/80CL51

STRONG PULL UP

2 OSCILLATOR PERIODS

+5V

P2

FROM

PORT

LATCH

Q

(a)

P1

P3

I/O PIN

n

INPUT DATA

READ PORT PIN

INPUT BUFFER

(b)

FROM

PORT

LATCH

Q

FROM

PORT

LATCH

Q

INPUT DATA

(c)

READ PORT PIN

STRONG PULL UP

+5V

P1

n

n

I/O PIN

+5V

I/O PIN

EXT.

PULL UP

INPUT BUFFER

Figure 3. Ports

The definition of port options for port 0 is slightly different. Two

cases have to be examined. First, accesses to external memory

(EA=0 or access above the built -in memory boundary), second, I/O

accesses.

External Memory Accesses

Option 1: True 0 and 1 are written as address to the external

memory (strong pull up is used).

Option 2: An external pull up resistor is needed for external

accesses.

Option 3: Not allowed for external memory access as the port can

only be used as output.

I/O Accesses

Option 1: When writing a 1 to the port-latch, the strong pull up p1

will be on for 2 oscillator periods. No weak pull up exists.

Without an external pull up, this option can be used as a

high-impedance input.

Option 2: Open drain; quasi-bidirectional I/O with n-channel open

drain output. Use as an output requires the connection of

an external pull up resistor (see Figure 3(c)).

Option 3: Push-Pull; output with drive capability in both polarities.

Under this option, pins can only be used as outputs.

Individual mask selection of the post-reset state is available on any

of the above pins. Make your selection by appending “S” or “R” to

option 1, 2, or 3 above (e.g. 1 S for a standard I/O to be set after

RESET or 2R for an open-drain I/O to be reset after RESET).

1.3 Timer/event counter

The 80CL51 contains two 16-bit Timer/Counter registers, Timer 0

and Timer 1, which can perform the following functions:

– Measure time intervals and pulse durations

– Count events

– Generate interrupts requests

January 1995

9

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