Owner manual

25 Rev. F - 15 February, 2001
T89C51RD2
Figure 8. PCA Interrupt System
PCA Modules: each one of the five compare/capture modules has six possible functions. It can perform:
• 16-bit Capture, positive-edge triggered,
• 16-bit Capture, negative-edge triggered,
• 16-bit Capture, both positive and negative-edge triggered,
• 16-bit Software Timer,
• 16-bit High Speed Output,
• 8-bit Pulse Width Modulator.
In addition, module 4 can be used as a Watchdog Timer.
Each module in the PCA has a special function register associated with it. These registers are: CCAPM0 for module
0, CCAPM1 for module 1, etc. (See Table 9). The registers contain the bits that control the mode that each module
will operate in.
• The ECCF bit (CCAPMn.0 where n=0, 1, 2, 3, or 4 depending on the module) enables the CCF flag in the
CCON SFR to generate an interrupt when a match or compare occurs in the associated module.
• PWM (CCAPMn.1) enables the pulse width modulation mode.
• The TOG bit (CCAPMn.2) when set causes the CEX output associated with the module to toggle when there
is a match between the PCA counter and the module's capture/compare register.
• The match bit MAT (CCAPMn.3) when set will cause the CCFn bit in the CCON register to be set when there
is a match between the PCA counter and the module's capture/compare register.
• The next two bits CAPN (CCAPMn.4) and CAPP (CCAPMn.5) determine the edge that a capture input will
be active on. The CAPN bit enables the negative edge, and the CAPP bit enables the positive edge. If both
bits are set both edges will be enabled and a capture will occur for either transition.
• The last bit in the register ECOM (CCAPMn.6) when set enables the comparator function.
Table 10 shows the CCAPMn settings for the various PCA functions.
.
CF CR
CCON
0xD8
CCF4 CCF3 CCF2 CCF1 CCF0
Module 4
Module 3
Module 2
Module 1
Module 0
ECF
PCA Timer/Counter
ECCFn
CCAPMn.0CMOD.0
IE.6 IE.7
To Interrupt
priority decoder
EC EA