Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

Design Considerations

A logic 1 from port A, bit 0 will turn the NPN transistor on, driving its collector low. The low level applied to the base of the PNP transistor, Q2, will drive its emitter to collector into conduction, illuminating the two LEDs. Resistor R5 is in place to guarantee that Q1 is biased off during initial power on and before the microcontroller’s program has configured port A, bit 1 to behave as a digital output.

5.4 Switch Circuitry

A simple circuit is used to give the ability of reading several switches into an A/D port. Figure 5-2shows the circuit. This circuit has the advantage of using only one I/O pin for the six switches. Using a switch matrix and the keyboard interrupt pins is an alternative approach, but in this case would require a microcontroller with more I/O pins.

Vdd

2

2

JP3

1

SW_DISC

1

 

R9

 

 

3.3K

 

 

POWER

 

PTA1_ATD1

SW1

 

 

 

 

 

R11

 

PLAY

4.7K

 

SW2

 

 

 

R12

 

FWD

2.2k

 

SW3

 

 

 

R15

 

REV

1k

 

SW6

 

 

 

R14

 

PAUSE

470

 

SW5

 

 

 

R13

 

STOP

220

 

SW4

 

Figure 5-2. Switch Circuitry

DRM045

Using the ASB520 MC68HC908QT2 Based Infrared Remote Control Reference PC Board

 

 

 

22

Design Considerations

MOTOROLA

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Freescale Semiconductor M68HC08, MC68HC908QT2 manual Design Considerations, Switch Circuitry

MC68HC908QT2, M68HC08 specifications

Freescale Semiconductor, known for its innovative solutions in the field of embedded systems, developed the M68HC08 microcontroller family, which includes the MC68HC908QT2. This 8-bit microcontroller is engineered to meet the demands of diverse applications, including automotive, industrial, and consumer electronics.

The MC68HC908QT2 is designed around Freescale’s M68HC08 core, which is renowned for its efficient and reliable performance. This microcontroller integrates a powerful instruction set, enabling developers to create high-performance applications with relatively low power consumption. The device operates at a clock frequency of up to 3 MHz, which is adequate for various control tasks.

One of the key features of the MC68HC908QT2 is its memory architecture. It includes a 2 KB Flash memory for program storage, representing a significant advantage for developers requiring non-volatile memory. Additionally, it encompasses 128 bytes of EEPROM memory, allowing for data retention even after power loss. The microcontroller also has 256 bytes of RAM for efficient data manipulation during operation.

In terms of input/output capabilities, the MC68HC908QT2 supports a variety of interfacing options. The microcontroller features up to 20 general-purpose I/O pins for flexibility in connecting with peripheral devices. Additionally, it provides multiple analog-to-digital converters (ADC) and timers that facilitate efficient analog signal processing and precise control through timing functions.

The architecture of the MC68HC908QT2 also incorporates sophisticated on-chip peripherals, enhancing its functionality. These peripherals include PWM (Pulse Width Modulation) outputs, which are essential for applications requiring motor control and other precise duty cycle processes. The integrated watchdog timer ensures reliable operation by resetting the system in the event of an application failure.

Moreover, the MC68HC908QT2 is equipped with an efficient power management system, enabling operation in a low-power mode, ideal for battery-powered applications. This microcontroller is packaged in a compact 28-pin dual in-line package (DIP), making it suitable for space-constrained designs.

In summary, the Freescale Semiconductor MC68HC908QT2 microcontroller is distinguished by its robust performance, extensive memory options, and versatile I/O capabilities. Its advanced features, including built-in timers, ADC, and a power management system, make it an exceptional choice for developers seeking to implement reliable and efficient embedded solutions. With its comprehensive architecture, the MC68HC908QT2 remains a popular choice in the landscape of 8-bit microcontrollers.