41
AT89C51RB2/RC2
4180E–8051–10/06
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 modules capture registers.
To activate this mode the TOG, MAT, and ECOM bits in the modules CCAPMn SFR
A prior write must be done to CCAPnL and CCAPnH before writing the ECOMn bit.
Figure 15. PCA High-speed Output Mode
Before enabling ECOM bit, CCAPnL and CCAPnH should be set with a non-zero value,
otherwise an unwanted match could occur.
Once ECOM is 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.
CH
CL
CCAPnH
CCAPnL
ECOMn
CCAPMn, n = 0 to 4
0xDA to 0xDE
CAPNn MATn TOGn PWMn ECCFn
CAPPn
16-bit Comparator
Match
CF
CR
CCON
0xD8
CCF4 CCF3
CCF2
CCF1
CCF0
PCA IT
Enable
CEXn
PCA Counter/Timer
Write to
CCAPnH
Reset
Write to
CCAPnL
1
0