Panasonic MN101C77C, F77G user manual bit Timer Count, Operation

Chapter 7 16-bit Timer

7-3 16-bit Timer Count

7-3-1 Operation

The timer operation can constantly generate interrupts.

„16-bit Timer Operation (Timer 7)

The generation cycle of an timer interrupt is set by the clock source selection and the set value of the compare register 1 (TM7OC1), in advance. When the binary counter (TM7BC) reaches the set value of the compare register 1, the timer 7 interrupt request is generated at the next count clock. There are 2 sources ; the TM7OC1 compare match or the full count over flow, to be selected to clear the binary counter. After the binary counter is cleared to x'0000, the counting up is restarted from x'0000'.

Table 7-3-1 16-bit Timer Interrupt Source and Binary Counter Clear Source (Timer 7)

TM7MD2 register		Interrupt source	Binary counter clear source
TM7IRS1 flag	TM7BCR flag
1	1	TM7OC1 compare match	TM7OC1 compare match
0	1	TM7OC1 compare match	TM7OC1 compare match
1	0	TM7OC1 compare match	full count over flow
0	0	full count over flow	full count over flow

Timer 7 can generate another set of an independent interrupt (Timer 7 compare register 2 match inter- rupt) by the set value of the timer 7 compare register (TM7OC2). At that timer, the binary counter is cleared as the above setup.

The compare register is double buffer type. So, when the value of the preset register is changed during the counting, the changed value is stored to the compare register as the binary counter is cleared. This function can change its value of the compare register constantly, without disturbing the cycle during timer operation (Reload function).

When the CPU reads the 16-bit binary counter (TM7BC), the read data is treated as 8-bits unit data even if it is a 16-bit MOVW instruction. As a result, it will read the data incorrectly if a carry from the lower 8 bits to the upper 8 bits occurs during counting.

To read the correct value of the 16-bit counting (TM7BC), use the writing program function to the input capture register (TM7IC). By writing to the TM7IC, the counting data of TM7BC can be stored to TM7IC to read out the correct counting data during operation.

[ Chapter 7-9-1. Operation (p.VII-34) ]

VII - 10 16-bit Timer Count