em78f644nso28s ELAN Microelectronics Corp, em78f644nso28s Datasheet - Page 124

• Manufacturer Part Number: em78f644nso28s
• Description: Flash Series 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

EM78F648/644/642/641/548/544/542/541N
8-Bit Microcontroller
114 •
6.9.3 PWM Period (PRDX : PRDA or PRDB)
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:
1) TMRX is cleared.
2) The PWMX pin is set to 1.
3) The PWM duty cycle is latched from DTA/DTB to DLA/DLB.
(4) The PWMXIF pin is set to “1”.
To calculate the PWM time period, use the following formula:
Example:
PRDX = 49; Fosc = 4 MHz, TMRX (0, 0, 0) = 1 : 2,
6.9.4 PWM Duty Cycle (DTX: DTA or DTB)
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 DLX
until the current value of DLX is equal to TMRX.
The following formula describes how to calculate the PWM duty cycle:
Example:
DTX = 10; Fosc = 4 MHz;
Then-
Then-
Duty
Period
cycle
The PWM output will not be set, if the duty cycle is “0”.
Period
=
Duty
(
PRDX
=
cycle
=
(
DTX
TMRX (0, 0, 0) = 1 : 2,
+
(
49
1
)
×
=
)
+
×
⎛
⎜
⎝
(This specification is subject to change without further notice)
1
⎛
⎜ ⎜
⎝
( )
Fosc
)
10
F
NOTE
1
×
OSC
1
×
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎜
⎝
⎞
⎟ ⎟
⎠
4
×
4
1
×
M
(
1
M
Product Specification (V1.0) 05.05.2010
TMRX
(
TMRX
⎞
⎟
⎠
⎞
⎟
⎠
×
×
2
2
prescaler
=
prescale
=
5
25
μs
μs
value
value
)
)