4 Modified Blank Signal

The example firmware and flow charts rely on the BLANK signal being manually toggled during a software interrupt. Using an interrupt allows the firmware to know when the BLANK signal is toggled and the end of a frame has been reached. This is useful when the microprocessor and software need to synchronize data transfers to correspond with the end of a display frame. If frame synchronization is not required, then the interrupt can be removed from the code which will free up the interrupt routine for other software functions. The capture and compare functions of the timer can be used to generate the BLANK signal without the need for the interrupt routine. This requires the timer to be configured slightly different than what is shown in the example firmware. The following four lines of code replace the four lines of code listed under the “SET UP TIMER TO MAKE BLANK SIGNAL” header in the code listing.

MOV.W #OUTMOD_3+CCIE,&CCTL0 ; CCR1 toggle/set MOV.W #4098,CCR0 MOV.W #4097,CCR1 MOV.W #TASSEL_2+MC_1,&TACTL ; turn on PWM - SMCLK, up mode

This code configures the counter timer to automatically toggle the BLANK line once the counter reaches 4097. With this code, the interrupts can be left disabled if desired.