T89C51RD2-3CBC-L ATMEL [ATMEL Corporation], T89C51RD2-3CBC-L Datasheet - Page 30

• Manufacturer Part Number: T89C51RD2-3CBC-L
• Description: 0 to 40MHz Flash Programmable 8-bit Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

Before enabling ECOM bit, CCAPnL and CCAPnH should be set with a non zero value, otherwise an unwanted
match could happen.
Once ECOM set, writing CCAPnL will clear ECOM so that an unwanted match doesn’t occur while modifying
the compare value. Writing to CCAPnH will set ECOM. For this reason, user software should write CCAPnL first,
and then CCAPnH. Of course, the ECOM bit can still be controlled by accessing to CCAPMn register.
6.5.4. Pulse Width Modulator Mode
All of the PCA modules can be used as PWM outputs. Figure 12 shows the PWM function. The frequency of the
output depends on the source for the PCA timer. All of the modules will have the same frequency of output
because they all share the PCA timer. The duty cycle of each module is independently variable using the module's
capture register CCAPLn. When the value of the PCA CL SFR is less than the value in the module's CCAPLn
Rev. F - 15 February, 2001
CCAPnH
Write to
1
CCAPnL
Write to
0
Reset
Enable
PCA counter/timer
CCAPnH
Figure 11. PCA High Speed Output Mode
CH
16 bit comparator
CF
ECOMn
CCAPnL
CR
CL
CAPPn
Match
CAPNn MATn TOGn PWMn ECCFn
CCF4 CCF3
CCF2
CCF1
T89C51RD2
CCF0
CCON
0xD8
CCAPMn, n = 0 to 4
0xDA to 0xDE
PCA IT
CEXn
30