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Freescale Semiconductor MC68HC908QT2 Freescale, Design Considerations, Introduction, Grounding

Models: M68HC08

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Section 5. Design Considerations

Semiconductor, Inc.

Freescale Semiconductor, Inc.

Designer Reference Manual — DRM045

Section 5. Design Considerations

5.1 Introduction

Microcontroller systems, in general, have a number of important design considerations related to PC board layout and grounding considerations. These design considerations are discussed in 5.2 Grounding, 5.3 Infrared and Visible LED Drive Circuit, and 5.4 Switch Circuitry. A description of two of the reference board’s major circuits are included in 5.3 Infrared and Visible LED Drive Circuit and 5.4 Switch Circuitry.

5.2 Grounding

PC board layout is an important design consideration. In particular, ground planes and how grounds are tied together influence noise immunity. To maximize oscillator noise immunity, it is a good practice have ground plane under the resonator, X1. One good grounding practice is to carry all of the ground connections, in a star configuration, to a single point which could be the power supply’s bulk capacitor or in this case, the battery ground terminal.

5.3 Infrared and Visible LED Drive Circuit

Figure 5-1is the driver schematic, used to drive both LEDs on the PC board. Because the microcontroller will not source or sink enough current to drive the two LEDs, a discrete driver is necessary. This circuit uses two transistors. The first transistor is a small signal NPN, followed by a small signal PNP transistor.

Freescale

		1	JP4	2
	To PTA0		1 2

IR_DISC

R5

47K

R4

1K

Vbat

R1

47K

R2Q2

3302N3906

Q1

2N3904

R6	R3
470	47
D2	D1

RED IR_LED

Figure 5-1. Infrared LED Drive Circuit

Using the ASB520 MC68HC908QT2 Based Infrared Remote Control Reference PC Board		DRM045

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Freescale Semiconductor MC68HC908QT2 manual Freescale, Design Considerations, Introduction, Grounding, Semiconductor, Inc

Contents

Freescale Semiconductor, Inc Freescale Semiconductor, IncUsing the ASB520 MC68HC908QT2 Based Infrared Remote Control Reference PC BoardFreescale Semiconductor, Inc Freescale Semiconductor, IncFor More Information On This Product Using the ASB520 MC68HC908QT2 Based Reference DesignInfrared Remote Control Reference PC Board Freescale Semiconductor, IncRevision History Revision HistoryFreescale Semiconductor, Inc Freescale Semiconductor, IncSection 1. Introduction and Setup Table of ContentsSection 4. Schematic and Parts List Section 6. System TestingFreescale Semiconductor, Inc Table of ContentsFreescale Semiconductor, Inc DRM0451.1 Introduction Section 1. Introduction and Setup1.2 About this Manual Freescale Semiconductor, Inc1.3 Setup Guide Introduction and SetupFreescale Semiconductor, Inc Freescale Semiconductor, IncIntroduction and Setup Introduction and Setup Setup GuideFreescale Semiconductor, Inc Freescale Semiconductor, IncFreescale Semiconductor, Inc Introduction and SetupFreescale Semiconductor, Inc DRM045Section 2. Operational Description 2.3.1 Red Activity Indicator LED2.1 Introduction 2.2 Push ButtonsFigure 2-1.PC Board Operational DescriptionFreescale Semiconductor, Inc JP1 JP2 JP3 JP42.4 Header and Jumpers Blocks Freescale Semiconductor, IncFreescale Semiconductor, Inc Freescale Semiconductor, Inc 2.5 Microcontroller Current Monitor Jumper BlockFreescale Semiconductor, Inc Operational DescriptionSection 3. Pin Description 3.2 16-PinConnector J13.1 Introduction Table 3-1.MON08 Pin AssignmentsFreescale Semiconductor, Inc Pin DescriptionFreescale Semiconductor, Inc DRM0454.2 Schematic Section 4. Schematic and Parts List4.1 Introduction Freescale Semiconductor, IncBoard Schematic Schematic and Parts ListSemiconductor, Inc Figure 4-1.ASB520 PCTable 4-1.Reference PC Board Parts List 4.3 Parts ListSchematic and Parts List Parts List Freescale Semiconductor, IncFreescale Semiconductor, Inc Schematic and Parts ListFreescale Semiconductor, Inc DRM045Section 5. Design Considerations Freescale5.1 Introduction 5.2 GroundingFigure 5-2.Switch Circuitry 5.4 Switch CircuitryDesign Considerations Freescale Semiconductor, IncDesign Considerations Switch Circuitry Table 5-1.Switch Input A/D ValuesSwitch Freescale Semiconductor, IncFreescale Semiconductor, Inc Freescale Semiconductor, IncDesign Considerations DRM0456.2 Hardware/Software Testing Summary Section 6. System Testing6.1 Introduction 6.3FLASH Programming6.4 LED and Push Button Test Code System TestingFreescale Semiconductor, Inc Freescale Semiconductor, Inc6.5 DVD Player Control Test Freescale Semiconductor, IncFreescale Semiconductor, Inc System Testing System TestingFreescale Semiconductor, Inc Freescale Semiconductor, IncFreescale Semiconductor, Inc Freescale Semiconductor, IncFor More Information On This Product Freescale Semiconductor, Inc HOW TO REACH USFreescale Semiconductor, Inc For More Information On This Product