HD404448 datasheet(62/125 Pages) RENESAS

62 / 125 page

HD404449 Series

Timer B Operations:

• Free-running/reload timer operation: The free-running/reload operation, input clock source, and

prescaler division ratio are selected by timer mode register B1 (TMB1: $009).

Timer B is initialized to the value set in timer write register B (TWBL: $00A, TWBU: $00B) by

software and incremented by one at each clock input. If an input clock is applied to timer B after it has

reached $FF, an overflow is generated. In this case, if the reload timer function is enabled, timer B is

initialized to its initial value set in timer write register B; if the free-running timer function is enabled,

the timer is initialized to $00 and then incremented again.

The overflow sets the timer B interrupt request flag (IFTB: $002, bit 0). IFTB is reset by software or

MCU reset. Refer to figure 3 and table 1 for details.

• External event counter operation: Timer B is used as an external event counter by selecting external

event input as the input clock source. In this case, pin R3

3/EVNB must be set to EVNB by port mode

Timer B is incremented by one at each falling edge of signals input to pin

EVNB. Other operations are

basically the same as the free-running/ reload timer operation.

• Timer output operation: The following three output modes can be selected for timer B by setting timer

mode register B2 (TMB2: $013).

 Toggle

 0 output

 1 output

By selecting the timer output mode, pin R3

0/TOB is set to TOB. The output from TOB is reset low by

MCU reset.

 Toggle output: When toggle output mode is selected, the output level is inverted if a clock is input

after timer B has reached $FF. By using this function and reload timer function, clock signals can

be output at a required frequency for the buzzer. The output waveform is shown in figure 43.

 0 output: When 0 output mode is selected, the output level is pulled low if a clock is input after

timer B has reached $FF. Note that this function must be used only when the output level is high.

 1 output: When 1 output mode is selected, the output level is set high if a clock is input after timer

B has reached $FF. Note that this function must be used only when the output level is low.

HD404448 Datasheet(PDF) 62 Page - Renesas Technology Corp