PIC16F676 - what is the Power-on Reset ?

[Micro_brain]

Power-on Reset

Dear Electronics Frindes
Please tell me
what is the Power-on Reset ?
I am useing PIC16F676
micr_brain

 

[btbass]

Power-on Reset

It is the state the SFR registers assume when powered up from cold.
For example, all I/O lines power up as inputs, the tris registers are all set to 1 on reset.

 

[saeed_pk]

Re: Power-on Reset

Whenever you apply power to any electronic circuit it take sometime for are devices to be Up for work. In the Power-On-Reset MCU remains reset until all the registers are Up. This time may very device to device

 

[VVV]

Re: Power-on Reset

A reset is required to establish a known state for the micro. A powe-on reset does eaclty that whenever it detects that power has just been applied. In the case of the PIC, this is done by sensing the Vdd voltage, which has to rise at a minimum rate for the POR to work, or else it will not recognize that power has just been applied. Once the circuit has detected a fast enough rate of change in Vdd it keeps the micro in reset for a given time, usually 18ms for the PIC. That is sufficient to ensure all the internal circuitry is reset.

 

[Micro_brain]

Re: Power-on Reset

Thanks frinds your replays
if so, what type relationship between WEAK PULL-UP,Power-on Reset ,power up timr and Tris.

I wrote in mycode

port_a_pullups(0b000001); // pull_up only PORTA bit 0
SET_TRIS_A(0b001111); // PORTA bit 4 and bit 5 as output

at startup.

but some time power is on,
PORTA bit 5 as input and pull_up enabled // wrong

(PORTA bit 5 I use for a Relay via Transister, by the wrong pull_up the Relay will on)
my config "#fuses WDT,INTRC_IO, PROTECT, BROWNOUT, NOMCLR, NOCPD, PUT "


in PIC16F676 Datasheet.
----------------------------
3.2.1 WEAK PULL-UP
Each of the PORTA pins, except RA3, has an individually
configurable weak internal pull-up. Control bits
WPUAx enable or disable each pull-up. Refer to
Register 3-3. Each weak pull-up is automatically turned
off when the port pin is configured as an output. The
pull-ups are disabled on a by the
RAPU bit (OPTION<7>).

Micro_brain