Datasheet

41
4235K–8051–05/08
AT89C51RD2/ED2
Table 13-4. PCA Module Modes (CCAPMn Registers)
There are two additional registers associated with each of the PCA modules. They are CCAPnH
and CCAPnL and these are the registers that store the 16-bit count when a capture occurs or a
compare should occur. When a module is used in the PWM mode these registers are used to
control the duty cycle of the output (See Table 13-5 & Table 13-6).
Table 13-5. CCAPnH Registers (n = 0 - 4)
CCAP0H - PCA Module 0 Compare/Capture Control Register High (0FAh)
CCAP1H - PCA Module 1 Compare/Capture Control Register High (0FBh)
CCAP2H - PCA Module 2 Compare/Capture Control Register High (0FCh)
CCAP3H - PCA Module 3 Compare/Capture Control Register High (0FDh)
CCAP4H - PCA Module 4 Compare/Capture Control Register High (0FEh)
Reset Value = 0000 0000b
Not bit addressable
ECOMn CAPPn CAPNn MATn TOGn PWMm ECCFn Module Function
0 0 0 0 0 0 0 No Operation
X 1 0 0 0 0 X
16-bit capture by a positive-edge
trigger on CEXn
X 0 1 0 0 0 X
16-bit capture by a negative trigger on
CEXn
X 1 1 0 0 0 X 16-bit capture by a transition on CEXn
1 0 0 1 0 0 X 16-bit Software Timer/Compare mode.
1 0 0 1 1 0 X 16-bit High Speed Output
1 0 0 0 0 1 0 8-bit PWM
1 0 0 1 X 0 X Watchdog Timer (module 4 only)
7 6 5 4 3 2 1 0
- - - - - - - -
Bit
Number
Bit
Mnemonic Description
7 - 0 -
PCA Module n Compare/Capture Control
CCAPnH Value