Change Register Bit Field Configurations using Bit Masks

When updating only a bit field in a register, a read-modify-write must be used, to keep the other settings unaffected. Therefore, in order to change the configuration of a register bit field, it is recommended to first clear the bit field and then set a new configuration. However, in order to avoid putting the register in an unintended state between the clear and setting the new configuration, this should be done in a single line of code. For simplicity, the steps are first covered individually.

The bit field masks can be used to clear a bit field before assigning a new configuration. In the example, the T0OUTPS bit field mask is used to clear bit field.

/* The T0OUTPS bit field is cleared (Selecting a postscaler of 1:1 (T0OUTPS = 0)) */
T0CON0 &= ~_T0CON0_T0OUTPS_MASK; 
/* Selecting new configuration (0b0111) of the T0OUTPS bit field */
T0CON0 |= _T0CON0_T0OUTPS2_MASK | _T0CON0_T0OUTPS1_MASK | _T0CON0_T0OUTPS0_MASK;  

The bit field mask for the TMR0 Output Postscaler Select (T0OUTPS) has the following declaration in the header file.

#define _T0CON0_T0OUTPS_MASK                               0xF

These steps must be implemented in a single line to avoid putting the microcontroller in an unintended state.

T0CON0 = (T0CON0 & ~_T0CON0_T0OUTPS_MASK) | _T0CON0_T0OUTPS2_MASK 
                                          | _T0CON0_T0OUTPS1_MASK 
                                          | _T0CON0_T0OUTPS0_MASK;