Philips Semiconductors

Preliminary data

P89C51RA2/RB2/RC2/RD2xx

80C51 8-bit Flash microcontroller family

8KB/16KB/32KB/64KB ISP/IAP Flash with 512B/512B/512B/1KB RAM

2002 Jul 18

37

CCAPMn Address

CCAPM0

0DAH

CCAPM1

0DBH

CCAPM2

0DCH

CCAPM3

0DDH

CCAPM4

0DEH

Reset Value = X000 0000B

–

ECOMn

CAPPn

CAPNn

MATn

TOGn

PWMn

ECCFn

Not Bit Addressable

Bit:

Symbol

Function

–

Not implemented, reserved for future use*.

ECOMn

Enable Comparator. ECOMn = 1 enables the comparator function.

CAPPn

Capture Positive, CAPPn = 1 enables positive edge capture.

CAPNn

Capture Negative, CAPNn = 1 enables negative edge capture.

MATn

Match. When MATn = 1, a match of the PCA counter with this module’s compare/capture register causes the CCFn bit

in CCON to be set, flagging an interrupt.

TOGn

Toggle. When TOGn = 1, a match of the PCA counter with this module’s compare/capture register causes the CEXn

pin to toggle.

PWMn

Pulse Width Modulation Mode. PWMn = 1 enables the CEXn pin to be used as a pulse width modulated output.

ECCFn

Enable CCF interrupt. Enables compare/capture flag CCFn in the CCON register to generate an interrupt.

NOTE:

*User software should not write 1s to reserved bits. These bits may be used in future 8051 family products to invoke new features In that case, the reset or inactive

value of the new bit will be 0, and its active value will be 1. The value read from a reserved bit is indeterminate.

SU01320

7654

321

0

Figure 30. CCAPMn: PCA Modules Compare/Capture Registers

–

ECOMn

CAPPn

CAPNn

MATn

TOGn

PWMn

ECCFn

MODULE FUNCTION

X

0

0

0

0

0

0

0

No operation

X

X

1

0

0

0

0

X

16-bit capture by a positive-edge trigger on CEXn

X

X

0

1

0

0

0

X

16-bit capture by a negative trigger on CEXn

X

X

1

1

0

0

0

X

16-bit capture by a transition on CEXn

X

1

0

0

1

0

0

X

16-bit Software Timer

X

1

0

0

1

1

0

X

16-bit High Speed Output

X

1

0

0

0

0

1

0

8-bit PWM

X

1

0

0

1

X

0

X

Watchdog Timer

Figure 31. PCA Module Modes (CCAPMn Register)

PCA Capture Mode

To use one of the PCA modules in the capture mode either one or

both of the CCAPM bits CAPN and CAPP for that module must be

set. The external CEX input for the module (on port 1) is sampled for

a transition. When a valid transition occurs the PCA hardware loads

the value of the PCA counter registers (CH and CL) into the

module’s capture registers (CCAPnL and CCAPnH). If the CCFn bit

for the module in the CCON SFR and the ECCFn bit in the CCAPMn

SFR are set then an interrupt will be generated. Refer to Figure 32.

16-bit Software Timer Mode

The PCA modules can be used as software timers by setting both

the ECOM and MAT bits in the modules CCAPMn register. The PCA

timer will be compared to the module’s capture registers and when a

match occurs an interrupt will occur if the CCFn (CCON SFR) and

the ECCFn (CCAPMn SFR) bits for the module are both set (see

Figure 33).

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 34).

Pulse Width Modulator Mode

All of the PCA modules can be used as PWM outputs. Figure 35

shows the PWM function. The frequency of the output depends on

the source for the PCA timer. All of the modules will have the same

frequency of output because they all share the PCA timer. The duty

cycle of each module is independently variable using the module’s

capture register CCAPLn. When the value of the PCA CL SFR is

less than the value in the module’s CCAPLn SFR the output will be

low, when it is equal to or greater than the output will be high. When

CL overflows from FF to 00, CCAPLn is reloaded with the value in

CCAPHn. the allows updating the PWM without glitches. The PWM

and ECOM bits in the module’s CCAPMn register must be set to

enable the PWM mode.