HT85F2270 datasheet(124/226 Pages) HOLTEK

124 / 226 page

Rev. 1.00

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

I/O Pin Structures

The accompanying diagrams illustrate the internal structures of some generic I/O pin types. As

the exact logical construction of the I/O pin will differ from these drawings, they are supplied as a

guide only to assist with the functional understanding of the I/O pins.

Quasi-bidirectional I/O – All Ports

This is the traditional 8051 type I/O port type, constructed from an NMOS FET transistor and

three pull high resistors, so called Strong, Weak, Very Weak pull high resistors. This structure can

be used to reduce the power consumption and the output switching state respond time.

A Very Weak pull high resistor will be turned on whenever the I/O port registers, associated with

the I/O pins, contain a high level.

When the I/O port registers has a high level and the corresponding I/O pins stay at high level as

well, the Weak pull high resistor will be turned on. However, if the I/O port registers are high and

the corresponding I/O pins are pulled low by the external devices, then the Weak pull high resistor

will be disabled by hardware. These weak pull-high resistor enable/disable function are dependant

on the voltage level after the I/O pin is connected to the external circuit.

The Strong pull high resistor is used to enhance the output response time. When the output state

changes from low to high, the Strong resistor will be turned on after two system clock delay times.

A Quasi-bidirectional pin also provides a Schmitt Trigger input.

Input

Data

Port Register Data

VCC

Strong

Two System

Clock Delay

VCC

Very Weak

VCC

Weak

Port

Quasi-bidirectional I/O Structure

HT85F2270 Datasheet(PDF) 124 Page - Holtek Semiconductor Inc