Hi.
I tryed  to use  PIC16C621A, RA4 as output, open drain. I put a 10K resistor
to Vcc and the base of a npn transistor in RA4 to drive a relay (relay
conected on colector with diode self induction protection, and emitter to
zero).
When the port come hight imediately drop to zero and sit there.
I saw that, when the output (in  RA4)drop to any value
<Vdd/2, by external circuit,  this output become to zero and stay in zero
even the value of the
external circuit apply in RA4 return to any value > Vdd/2.
I made a test.
The output is high, and I force pin 3 ( RA4 ) with a
jump to zero. The current is limited by 10K resistor to Vdd. When I remove
this jump the output stays in zero ! Note, by the program this output is
high all the time .
The same test in a PIC16F84 this do not happen (no comparator sets!). The
output come to zero with a jump to zero and return to high when remove this
jump.
Anyone knows why this happen ?
I didn't find nothing in data sheet (16C621A) about it.
My sets:
 banc1                                       ;macro to bank 1
 MOVLW  b'00000010'           ;Place option reg setup into W
 MOVWF  OPTION_REG       ; Set up OPTION register
 MOVLW   b'00000011'           ; RA0 and RA1 as intput RA2,3 and 4 as output
 MOVWF  TRISA                      ;
 banc0                                        ;macro to bank 0
 MOVLW  b'00000111'            ;07h comparator off
 MOVWF  CMCON
 MOVLW  B'10100000'            ; int only to tmr0
 MOVWF  INTCON
VRCON, I left by default. (b'00000000')

Did I forgot any set?
TIA
Roberto Locks Guimaraes

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.