Philips P89LPC907 用户手册

2003 Dec 8     

75

 If the comparator output to a pin is enabled, the pin should be configured in the push-pull mode in order to obtain fast switching 
times while in power down mode. The reason is that with the oscillator stopped, the temporary strong pullup that normally occurs 
during switching on a quasi-bidirectional port pin does not take place.

The comparator consumes power in Power down and Idle modes, as well as in the normal operating mode. This fact should be 
taken into account when system power consumption is an issue. To minimize power consumption, the user can disable the 
comparator via PCONA.5 or put the device in Total Power down mode.

The code shown below is an example of initializing the comparator. This comparator  is configured to use the CMPREF inputs. 
The comparator output drives the CMP pin and generates an interrupt when the comparator output changes.

CMPINIT:

MOV

PT0AD,#030h

; Disable digital INPUTS on pins that are used 

; for analog functions: CIN, CMPREF.

ANL

P0M2,#0CFh

; Disable digital OUTPUTS on pins that are used

ORL

P0M1,#030h

; for analog functions: CIN, CMPREF.

MOV

CMP1,#024h

; Turn on comparator  and set up for:

; - Negative input from CMPREF pin.

; - Output to CMP pin enabled.

CALL

delay10us

; The comparator has to start up for at 

; least 10 microseconds before use.

ANL

CMP1,#0FEh

; Clear comparator interrupt flag.

SETB

EC

; Enable the comparator interrupt. The 

; priority is left at the current value.

SETB

EA

; Enable the interrupt system (if needed).

RET

; Return to caller.

The interrupt routine used for the comparator must clear the interrupt flag (CMF1 in this case) before returning.