DS80C310

4 of 22

PIN

PDIP

PLCC

TQFP

NAME

FUNCTION

Port 3 (I/O). Port 3 functions as both an 8-bit bidirectional I/O port

and an alternate functional interface for external Interrupts, Serial

Port 0, Timer 0 and 1 Inputs,

RD and WR strobes. The reset

condition of Port 3 is with all bits at logic 1. In this state, a weak

pullup holds the port high. This condition also serves as an input

mode, since any external circuit that writes to the port will overcome

the weak pullup. When software writes a 0 to any port pin, the

DS80C310 will activate a strong pulldown that remains on until

either a 1 is written or a reset occurs. Writing a 1 after the port has

been at 0 will cause a strong transition driver to turn on, followed by

a weaker sustaining pullup. Once the momentary strong driver turns

off, the port once again becomes both the output high and input

state. The alternate modes of Port 3 are as follows:

PIN

PDIP

PLCC

TQFP

PORT

ALTERNATE

FUNCTION

10

11

5

P3.0

RXD0

Serial Port 0

Input

11

13

7

P3.1

TXD0

Serial Port 0

Output

12

14

8

P3.2

INT0

External Interrupt

0

13

15

9

P3.3

INT1

External Interrupt

1

14

16

10

P3.4

T0

Timer 0 External

Input

15

17

11

P3.5

T1

Timer 1 External

Input

16

18

12

P3.6

WR

External Data

Memory Write

Strobe

10–17

11,

13–19

5, 7–13

P3.0–P3.7

17

19

13

P3.7

RD

External Data

Memory Read

Strobe

18, 19

20, 21

14, 15

XTAL2,

XTAL1

Crystal Oscillator Pins. XTAL1 and XTAL2 provide support for

parallel resonant, AT-cut crystals. XTAL1 also acts as an input in

the event that an external clock source is used in place of a crystal.

XTAL2 serves as the output of the crystal amplifier.

20

1, 22,

23

16, 17,

39

GND

Digital Circuit Ground

21

24

18

A8(P2.0)

22

25

19

A9(P2.1)

23

26

20

A10(P2.2)

24

27

21

A11(P2.3)

25

28

22

A12(P2.4)

26

29

23

A13(P2.5)

27

30

24

A14(P2.6)

28

31

25

A15(P2.7)

Address Outputs (Port 2) (Output). Port 2 serves as the MSB for

external addressing. P2.7 is A15 and P2.0 is A8. The DS80C310

automatically places the MSB of an address on P2 for external ROM

and RAM access. Although Port 2 can be accessed like an ordinary

I/O port, the value stored on the Port 2 latch is never seen on the pins

(due to memory access). Therefore, writing to Port 2 in software is

only useful for the instructions MOVX A, @ Ri or MOVX @ Ri, A.

These instructions use the Port 2 internal latch to supply the external

address MSB; the Port 2 latch value is supplied as the address

information.