DS80C320-ENG datasheet(4/40 Pages) MAXIM

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DS80C320/DS80C323 High-Speed/Low-Power Microcontrollers

4 of 40

PIN DESCRIPTION (continued)

DIP

PLCC

TQFP

NAME

FUNCTION

ALE

Address Latch-Enable Output. This pin functions as a clock to latch

the external address LSB from the multiplexed address/data bus. This

signal is commonly connected to the latch enable of an external 373

family transparent latch. ALE has a pulse width of 1.5 XTAL1 cycles

and a period of four XTAL1 cycles. ALE is forced high when the

device is in a reset condition.

AD0

AD1

AD2

AD3

AD4

AD5

AD6

AD7

Port 0, Input/Output. Port 0 is the multiplexed address/data bus.

During the time when ALE is high, the LSB of a memory address is

presented. When ALE falls, the port transitions to a bi-directional data

bus. This bus is used to read external ROM and read/write external

RAM memory or peripherals. The Port 0 has no true port latch and

cannot be written directly by software. The reset condition of Port 0 is

high. No pullup resistors are needed.

Port 1, I/O. Port 1 functions as both an 8-bit, bidirectional I/O port and

an alternate functional interface for Timer 2 I/O, new External

Interrupts, and new Serial Port 1. The reset condition of Port 1 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 the output high (and

input) state. The alternate modes of Port 1 are outlined as follows:

DIP

PLCC

TQFP

PORT

ALTERNATE

FUNCTION

P1.0

External I/O for

Timer/Counter 2

P1.1

T2EX

Timer/Counter 2

Capture/Reload Trigger

P1.2

RXD1

Serial Port 1 Input

P1.3

TXD1

Serial Port 1 Output

P1.4

INT2

External Interrupt 2

(Positive-Edge Detect)

P1.5

INT3

External Interrupt 3

(Negative-Edge Detect)

P1.6

INT4

External Interrupt 4

(Positive-Edge Detect)

1–8

2–9

40–44,

1–3

P1.0–P1.7

P1.7

INT5

External Interrupt 5

(Negative-Edge Detect)

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