SyncMOS Technologies International. Inc.
SM79108
1st cycle frame 2nd cycle frame 3rd cycle frame 4th cycle frame 5th cycle frame
6th cycle frame 7th cycle frame 8th cycle frame
32T
32T
32T
32T
32T
32T
32T
32T
16T
16T
16T
16T
16T
16T
16T
16T
1T
1T
1T
(narrow pulse inserted by BRM0[2:0] setting, here BRM0[2:0]=3)
SPWM clock = 1 / T = Fosc / 2^(SPFS[1:0]+1)
The SPWM output cycle frame frequency = SPWM clock / 32 = [Fosc/2^(SPFS[1:0]+1)]/32
If user use Fosc=20MHz, SPFS[1:0] of SPWMC=#03H, then
SPWM clock = 20MHz/2^4 = 20MHz/16 = 1.25MHz
SPWM output cycle frame frequency = (20MHz/2^4)/32=39.1KHz
5. PWM Function Description:
Each PWM channel contains a 8-bit wide PWM data register (PWMDR) to decide number of continuous pulses within a
PWM frame cycle. The value programmed in the register will determine the pulse length of the output. The PWM channel
can be configured as 5-bit or 8-bit resolution. If a channel is configured as 5-bit resolution, only LSB 5 bits are available.
The value of each PWM Data Register (PWMDR) is continuously compared with the content of an internal counter to deter-
mine the state of each PWM channel output pin.
5.1 PWM Registers - PWMC0, PWMD0
PWM Registers - PWM Control Register (PWMC0, 0D3H)
bit-7
bit-0
PFS0
R/W
0
Unused
Unused
Unused
Unused
Unused
PBS
R/W
0
PFS1
R/W
0
Read / Write:
Reset value:
-
-
-
-
-
*
*
*
*
*
PFS[1:0]: These two bits is 2’s power parameter to form a frequency divider for input clock.
PBS: This bit decides channel bit resolution. If PBS is set, the channel is 5-bit resolution.
PFS1
PFS0
Divider
16
PWM clock, Fosc=12MHz
750KHz
PWM clock, Fosc=24MHz
1.5MHz
0
0
1
1
0
1
0
1
32
375KHz
750KHz
64
187.5KHz
375KHz
128
93.75KHz
187.5KHz
Example : If user use Fosc = 20MHz, PFS[1:0] of PWMC = #03H, PBS = 0, then
PWM Clock = 20MHz / 128 = 156.25KHz
PWM Output cycle frame frequency = 156.25KHz / 256 = 610 Hz
Note : For bzzer application
Specifications subject to change without notice,contact your sales representatives for the most recent information.
10/26
Ver 2.1 SM79108 08/2006
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
