Philips Semiconductors

Preliminary specification

OM5234/OM5284

CMOS single-chip 8-bit microcontrollers

1996 Nov 01

4

PIN DESCRIPTIONS

PIN NUMBER

MNEMONIC PLCC

QFP

DIP

TYPE

NAME AND FUNCTION

22

6, 16,

28, 39

20

I

connected.

44

38

40

I

Power Supply: This is the power supply voltage for normal, idle, and power-down

operation.

P0.0–0.7

43–36

37–30

39–32

I/O

Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that have 1s written to

them float and can be used as high-impedance inputs. Port 0 is also the multiplexed

low-order address and data bus during accesses to external program and data memory.

In this application, it uses strong internal pull-ups when emitting 1s.

P1.0–P1.7

2–9

40–44,

1–3

1–8

I/O

Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups, except P1.6 and P1.7,

which are open drain for OM5234 (only). Port 1 pins that have 1s written to them are

pulled high by the internal pull-ups and can be used as inputs. As inputs, port 1 pins that

are externally pulled low will source current because of the internal pull-ups. (See DC

P1.6

8

2

7

I/O

Bidirectional I/O with internal pull-ups (OM5284), and open drain for (OM5234).

P1.7

9

3

8

I/O

Bidirectional I/O with internal pull-ups (OM5284), and open drain for (OM5234).

P2.0–P2.7

24–31

18–25

21–28

I/O

Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 pins that have

1s written to them are pulled high by the internal pull-ups and can be used as inputs. As

inputs, port 2 pins that are externally being pulled low will source current because of the

address byte during fetches from external program memory and during accesses to

external data memory that use 16-bit addresses (MOVX @DPTR). In this application, it

uses strong internal pull-ups when emitting 1s. During accesses to external data memory

that use 8-bit addresses (MOV @Ri), port 2 emits the contents of the P2 special function

register.

P3.0–P3.7

11,

13–19

5,

7–13

10–17

I/O

Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 pins that have

1s written to them are pulled high by the internal pull-ups and can be used as inputs. As

inputs, port 3 pins that are externally being pulled low will source current because of the

the 80C51 family, as listed below:

11

5

10

I

RxD (P3.0): Serial input port

13

7

11

O

TxD (P3.1): Serial output port

14

8

12

I

INT0 (P3.2): External interrupt

15

9

13

I

INT1 (P3.3): External interrupt

16

10

14

I

T0 (P3.4): Timer 0 external input

17

11

15

I

T1 (P3.5): Timer 1 external input

18

12

16

O

WR (P3.6): External data memory write strobe

19

13

17

O

RD (P3.7): External data memory read strobe

RST

10

4

9

I

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

ALE

33

27

30

I/O

Address Latch Enable: 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

the oscillator frequency. Note that one ALE pulse is skipped during each access to

external data memory.

PSEN

32

26

29

O

Program Store Enable: Read strobe to external program memory via Port 0 and Port 2.

It is activated twice each machine cycle during fetches from the external program

memory. When executing out of external program memory, two activations of PSEN are

skipped during each access to external data memory. PSEN is not activated (remains

HIGH) during fetches from external program memory. PSEN can sink/source 8 LSTTL

inputs and can drive CMOS inputs without external pull-ups.

EA

35

29

31

I

External Access: If during a RESET, EA is held at TTL, level HIGH, the CPU executes

out of the internal program memory ROM provided the Program Counter is less than

16384. If during a RESET, EA is held at TTL LOW level, the CPU executes out of external

program memory. EA is not allowed to float.

XTAL1

21

15

19

I

Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock

generator circuits.

XTAL2

20

14

18

O

Crystal 2: Output from the inverting oscillator amplifier.

NOTE: