Z8F082ASJ020EG Datasheet, PDF(56/282 Page) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

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Z8F082ASJ020EG Datasheet, PDF (56/282 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

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Z8 Encore! XPÂ® F082A Series

Product Specification

39

Shared Debug Pin

On the 8-pin version of this device only, the Debug pin shares function with the PA0 GPIO

pin. This pin performs as a general purpose input pin on power-up, but the debug logic

monitors this pin during the reset sequence to determine if the unlock sequence occurs. If

the unlock sequence is present, the debug function is unlocked and the pin no longer func-

tions as a GPIO pin. If it is not present, the debug feature is disabled until/unless another

reset event occurs. For more details, see the On-Chip Debugger chapter on page 180.

Crystal Oscillator Override

For systems using a crystal oscillator, PA0 and PA1 are used to connect the crystal. When

the crystal oscillator is enabled, the GPIO settings are overridden and PA0 and PA1 are

disabled. See the Oscillator Control Register Definitions section on page 196 for details.

5 V Tolerance

All six I/O pins on the 8-pin devices are 5 V-tolerant, unless the programmable pull-ups

are enabled. If the pull-ups are enabled and inputs higher than VDD are applied to these

parts, excessive current flows through those pull-up devices and can damage the chip.

Note:

In the 20- and 28-pin versions of this device, any pin which shares functionality with an

ADC, crystal or comparator port is not 5 V-tolerant, including PA[1:0], PB[5:0] and

PC[2:0]. All other signal pins are 5 V-tolerant and can safely handle inputs higher than

VDD except when the programmable pull-ups are enabled.

External Clock Setup

For systems using an external TTL drive, PB3 is the clock source for 20- and 28-pin

devices. In this case, configure PB3 for alternate function CLKIN. Write the Oscillator

Control (OSCCTL) Register such that the external oscillator is selected as the system

clock. See the Oscillator Control Register Definitions section on page 196 for details. For

8-pin devices, use PA1 instead of PB3.

PS022827-1212

PRELIMINARY

Shared Debug Pin

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