DS80C320-ENG datasheet(5/38 Pages) MAXIM

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DS80C320/DS80C323 High-Speed/Low-Power Microcontrollers

5 of 38

PIN DESCRIPTION (continued)

DIP

PLCC

TQFP

NAME

FUNCTION

A8 (P2.0)

A9 (P2.1)

A10 (P2.2)

A11 (P2.3)

A12 (P2.4)

A13 (P2.5)

A14 (P2.6)

A15 (P2.7)

Port 2, Output. Port 2 serves as the MSB for external addressing.

P2.7 is A15 and P2.0 is A8. The device will automatically place 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 will never be 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. In this case, the Port 2 latch value will be supplied as the

address information.

Port 3, Input/Output. 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 & 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 device

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 outlined below:

DIP

PLCC

TQFP

PORT

ALTERNATE

MODE

P3.0

RXD0

Serial Port 0 Input

P3.1

TXD0

Serial Port 0 Output

P3.2

INT0

External Interrupt 0

P3.3

INT1

External Interrupt 1

P3.4

Timer 0 External Input

P3.5

Timer 1 External Input

P3.6

External Data Memory Write

Strobe

10–17

11, 13–

5, 7–13

P3.0–P3.7

P3.7

External Data Memory Read

Strobe

External Access, Active-Low Input. This pin must be connected to

ground for proper operation.

—

12, 34,

6, 28,

39*

N.C.

No Connection (Reserved). These pins should not be connected.

They are reserved for use with future devices in this family.

*These pins are reserved for additional ground pins on future products.

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