AT89C51RB2/RC2
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
must be set (see Figure 15).
A prior write must be done to CCAPnL and CCAPnH before writing the ECOMn bit.
Figure 15. PCA High-speed Output Mode
CCON
CF
CR
CCF4 CCF3 CCF2 CCF1 CCF0
0xD8
Write to
CCAPnL
Reset
PCA IT
Write to
CCAPnH
CCAPnH
CCAPnL
0
Enable
1
Match
16-bit Comparator
CEXn
CH
CL
PCA Counter/Timer
CCAPMn, n = 0 to 4
0xDA to 0xDE
ECOMnCAPPn CAPNn MATn TOGn PWMn ECCFn
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.
41
4180E–8051–10/06
ATMEL [ ATMEL ]
