definite port states at power-up
Hello everyone.
I have an application that must absolutely power-up in a definite state. Pins on port b must NOT be in high state. Output and low state is OK, input is ok.
The problem I am facing is that 1 time out of 1000, the pic will power up with a pin on port b being high for a few milliseconds, which is unacceptable.
This problem is driving me crazy, I have the power up timer enabled, pull down resistors on all pins, but still this pops up once in a while.
I wonder if this can ever be corrected in software or if I should consider a hardware solution (i.e. power the pic first, then power the rest of the circuit?)
Basically, my application waits for serial com and will pulse outputs accorrding to what message comes in. However, the short "high" state at power up happens even if no coms are coming in. Could it be garbage in the receive buffer being interpreted as valid data?
Should I clear the buffer before enabling interrupts? Could it be related to the voltage ramp-up time?
Any suggestions you may have would be greatly welcomed.
I have attached the first part of my program here, I am using a pic 16f877A:
@ __config _HS_OSC & _WDT_ON & _PWRTE_ON & _LVP_OFF & _CP_OFF & _BODEN_OFF
include "modedefs.bas"
TRISB=0
TRISC=%11111111
TRISD=0
PORTD=%00000000
portb=%00000000
ADCON1=%00000111 'PORT A AND PORT E ARE DIGITAL
DEFINE SER2_BITS 9 ' define 8 bits + parity
DEFINE HSER_RCSTA 90h 'receiver enabled
DEFINE HSER_BAUD 4800 'define 4800 baud speed
DEFINE HSER_CLROERR 1 'automatically clears buffer overrun errors
RCIF VAR PIR1.5 ' Alias RCIF (USART Receive Interrupt Flag)
OERR VAR RCSTA.1 ' Alias OERR (USART Overrun Error Flag)
CREN VAR RCSTA.4 ' Alias CREN (USART Continuous Receive Enable)
buffer_size CON 64 ' Sets the size of the ring buffer
addressbuffer VAR BYTE[buffer_size] ' Array variable for holding received characters
commandbuffer VAR BYTE[buffer_size] ' Array variable for holding received characters
index_in VAR BYTE ' Pointer - next empty location in buffer
index_out VAR BYTE ' Pointer - location of oldest character in buffer
bufchar VAR BYTE ' Stores the character retrieved from the buffer
i VAR BYTE ' loop counter
errflag VAR BYTE ' Holds error flags
ADDRESS var BYTE
COMMAND VAR BYTE
LOWADD VAR word
HIGHADD VAR word
value var byte
BOXADD VAR BYTE
loopcount var word
counter var byte[16]
loop var byte
fireflag var byte
OUTPUT_ENABLE VAR PORTA.1
clock var portE.0
datain var portA.3
load var portA.5
checkstatus var portE.1
dumpvar var byte
fireflag=0
VALUE=0
counter=0
high load
low checkstatus
low output_enable
index_in = 0
index_out = 0
i = 0
INTCON = %11000000 ' Enable interrupts
PIE1.5 = 1 ' Enable interrupt on USART
ON INTERRUPT GoTo serialin ' Declare interrupt handler routine
main:
IF errflag Then error ' Handle error if needed
IF index_in = index_out Then main
GoSub getbuf ' Get a character from buffer
ELSE
GOTO MAIN
ENDIF
‘(I haven’t included the whole program for sake of clarity)
