Rainbow Electronics T89C51RD2 - Manual (Page 29)

29 Rev. F - 15 February, 2001
T89C51RD2
Figure 10. PCA Compare Mode and PCA Watchdog Timer
Before enabling ECOM bit, CCAPnL and CCAPnH should be set with a non zero value, otherwise an unwanted
match could happen. Writing to CCAPnH will set the ECOM bit.
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.
6.5.3. High Speed Output Mode
In this mode the CEX output (on port 1) associated with the PCA module will toggle each time a match occurs
between the PCA counter and the module's capture registers. To activate this mode the TOG, MAT, and ECOM
bits in the module's CCAPMn SFR must be set (See Figure 11).
A prior write must be done to CCAPnL and CCAPnH before writing the ECOMn bit.
CH CL
CCAPnH CCAPnL
ECOMn
CCAPMn, n = 0 to 4
0xDA to 0xDE
CAPNn MATn TOGn PWMn ECCFn CAPPn
16 bit comparator
Match
CCON
0xD8
PCA IT
Enable
PCA counter/timer
RESET *
CIDL CPS1 CPS0 ECF
CMOD
0xD9
WDTE
*
Only for Module 4
Reset
Write to
CCAPnL
Write to
CCAPnH
CF CCF2 CCF1 CCF0 CR CCF3 CCF4
1 0