Question

Write the C-language instructions to: 4. Configure port D, pins 0-4 for output and 5-7 for input. Enable pull-up resistance on pins 5 and 6.

Answer 1

To configure a port as input or output DDRx instruction is used. If the particular pin has value 0 then it is configured as input, if 1 is set then it is configured as output. For first 5 pins to be set as output we need 11111 value, for 5-7 pins as input we need 000. First bit starts from right and last bit ends towards the left.

DDRD =0b00011111;

Converting to hex,

DDRD = 0x1F; //serves required purpose

To enable pull-up resistance on input pins use PORTx instruction. If a PIN is set to 1 in PORT instruction, the enable resistance is enabled. If it has a value 0 then the pull-up resistance is disabled. If disabled, the PINs go in tri-state where their value cant be determined which can lead to problems in circuit further. To enable PIN 5 and 6, set them to 1 in PORTx.

PORTD = 0b01100000;

PORTD = 0x60;

These instructions serve the purpose,

DDRD = 0x1F;

PORTD = 0x60;