Is there a way to write only the lower 4 bits of a byte on Port D (PD0 -PD3) ?.
The 4 bits are generated from a loop counter, and are used to drive a 16:1 74LS154 mutliplexer to select the CS of multiple SPI devices.
I am using Timer0 and Timer1 external interrupts (same pins as PD4 and PD5) and therefore want to avoid writing the whole byte.
I cannot use Port B as I am using the SPI for read and write (SCK, MISO, MOSI), which leaves only 3 bits available.
I cannot use Port C as I am using the I2C (SDA, SCL) to drive a display, and serval analogue inputs (ADC0 to ADC2).
Thanks