EM78459AM datasheet(41/62 Pages) EMC

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EM78458/459

8-Bit Microcontroller with MASK ROM

Product Specification (V1.4) 05.27.2005

• 35

(This specification is subject to change without further notice)

4.8.2 Increment Timer Counter ( TMRX: TMR1H/TWR1L or

TMR2H/TWR2L )

TMRX are ten-bit clock counters with programmable prescalers. They are designed for

the PWM module as baud rate clock generators. TMRX can be read, written, and

cleared at any reset conditions. If employed, they can be turned down for power saving

by setting T1EN bit [PWMCON<4>] or T2EN bit [PWMCON<5>] to 0.

4.8.3 PWM Period ( PRDX : PRD1 or PRD2 )

The PWM period is defined by writing to the PRDX register. When TMRX is equal to

PRDX, the following events occur on the next increment cycle:

TMRX is cleared.

The PWMX pin is set to 1.

The PWM duty cycle is latched from DT1/DT2 to DTL1/DTL2.

NOTE

The PWM output will not be set, if the duty cycle is 0;

The PWMXIF pin is set to 1.

The following formula describes how to calculate the PWM period:

PERIOD = (PRDX + 1) * 4 * (1/Fosc) * (TMRX prescale value )

4.8.4 PWM Duty Cycle ( DTX: DT1H/ DT1L and DT2H/ DT2L; DTL:

DL1H/DL1L and DL2H/DL2L )

The PWM duty cycle is defined by writing to the DTX register, and is latched from DTX

to DLX while TMRX is cleared. When DLX is equal to TMRX, the PWMX pin is cleared.

DTX can be loaded at any time. However, it cannot be latched into DTL until the

current value of DLX is equal to TMRX.

The following formula describes how to calculate the PWM duty cycle:

Duty Cycle = (DTX) * (1/Fosc) * (TMRX prescale value )

4.8.5 Comparator X

To change the output status while the match occurs, the TMRXIF flag will be set at the

same time.

4.8.6 PWM Programming Procedures/Steps

(1) Load PRDX with the PWM period.

(2) Load DTX with the PWM Duty Cycle.

(3) Enable interrupt function by writing IOCF0, if required.

EM78459AM Datasheet(PDF) 41 Page - ELAN Microelectronics Corp