I/O Registers, 6.2 ANx | Freescale Semiconductor MC68HC908MR16

I/O Registers

3.6.5 ADC Voltage In (ADVIN)

ADVIN is the input voltage signal from one of the 10 ADC channels to the ADC module.

3.6.6 ADC External Connections

This section describes the ADC external connections: VREFH and VREFL, ANx, and grounding.

3.6.6.1VREFH and VREFL

Both ac and dc current are drawn through the VREFH and VREFL loop. The AC current is in the form of current spikes required to supply charge to the capacitor array at each successive approximation step.

The current flows through the internal resistor string. The best external component to meet both these current demands is a capacitor in the 0.01 ∝F to 1 ∝F range with good high frequency characteristics. This

capacitor is connected between VREFH and VREFL and must be placed as close as possible to the package pins. Resistance in the path is not recommended because the dc current will cause a voltage

drop which could result in conversion errors.

3.6.6.2 ANx

Empirical data shows that capacitors from the analog inputs to VREFL improve ADC performance. 0.01-∝F and 0.1-∝F capacitors with good high-frequency characteristics are sufficient. These capacitors must be placed as close as possible to the package pins.

3.6.6.3 Grounding

In cases where separate power supplies are used for analog and digital power, the ground connection between these supplies should be at the VSSAD pin. This should be the only ground connection between these supplies if possible. The VSSA pin makes a good single point ground location. Connect the VREFL pin to the same potential as VSSAD at the single point ground location.

3.7 I/O Registers

These I/O registers control and monitor operation of the ADC:

•ADC status and control register, ADSCR

•ADC data registers, ADRH and ARDL

•ADC clock register, ADCLK

MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1

Freescale Semiconductor

MC68HC908MR16, MC68HC908MR32 specifications

Freescale Semiconductor's MC68HC908MR32 and MC68HC908MR16 microcontrollers are part of the popular HC08 family, designed primarily for embedded applications. These microcontrollers are particularly favored in automotive, industrial, and consumer product sectors due to their reliability and versatility.

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The MC68HC908MR32 variant is equipped with 32KB of flash memory, which allows for the storage of complex programs and extensive data handling. In contrast, the MC68HC908MR16 features 16KB of flash memory, making it ideal for simpler applications. Both microcontrollers also come with 1KB of RAM, enabling efficient data processing and real-time operations.

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Freescale Semiconductor MC68HC908MR16 I/O Registers, ADC Voltage In Advin, 6.2 ANx, Grounding

Models: MC68HC908MR16 MC68HC908MR32