14

7903A – AVR – 2006/02

True 1.8V Memory Operation

The processes used in AVR MCUs support a power supply voltage range from 1.8 to 5.5V.

The 1.8V operation is a true 1.8V operation. This means that all the analog modules,

Flash, EEPROM and RAM run at 1.8V enabling really low power applications. The wide

power supply range utilizes the complete battery life in a battery-driven application.

Pin Leakage and Digital Input Disable Register

AVR controllers mix ADC and digital I/O on the same pins. Using one ADC and a

multiplexed input, the microcontroller scans a number of pins. Multiplexing adds flexibility

to low pin-count devices but raises increase power consumption. A digital input is basically

built by two transistors, creating an input buffer as shown in Figure 8. As long as valid high

or low voltage levels are applied to the buffer, there is no problem. However, applying

voltages in the area of Vcc/2 will create a leakage current through the buffer as both

transistors will open slightly.

Figure 8: AVR mixed analog and digital I/O

Since the analog voltage level present at the input adds static power consumption, it is

important that the microcontroller be able to disable the digital input. Automatic disabling

based on the ADC’s multiplexer is not possible since the multiplexer is controlled by the

microcontroller’s firmware and is not predictable by the microcontroller itself. AVR

controllers solve this problem with a Dedicated Input Disable Register, DIDR, with one

disable bit per analog input.