OPTION_REG datasheet(85/222 Pages) MICROCHIP

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DS22331A-page 85

MCP19111

14.3

Power-up Timer (PWRT)

The Power-up Timer provides a fixed 64 ms (nominal)

time-out on power-up only, from POR Reset. The

Power-up Timer operates

from an internal RC

oscillator. The chip is kept in Reset as long as PWRT is

active. The PWRT delay allows the VDD to rise to an

acceptable level. A Configuration bit (PWRTE), can

disable (if set) or enable (if cleared or programmed) the

Power-up Timer.

The Power-up Timer delay will vary from chip-to-chip

due to:

•VDD variation

• Temperature variation

• Process variation

14.4

Watchdog Timer (WDT) Reset

The Watchdog Timer generates a Reset if the firmware

does not issue a CLRWDT instruction within the time-out

period. The TO and PD bits in the STATUS register are

changed to indicate the WDT Reset. See Section 17.0

“Watchdog Timer (WDT)” for more information.

14.5

Power-Up Timer

The Power-up Timer optionally delays device execution

after a POR event. This timer is typically used to allow

VDD to stabilize before allowing the device to start

running.

The Power-up Timer is controlled by the PWRTE bit of

Configuration Word.

14.6

Start-up Sequence

Upon the release of a POR, the following must occur

before the device will begin executing:

• Power-up Timer runs to completion (if enabled)

• Oscillator start-up timer runs to completion

•MCLR must be released (if enabled)

The total time-out will vary based on PWRTE bit status.

For example, with PWRTE bit erased (PWRT disabled),

there will be no time-out at all. Figures 14-3, 14-4

and 14-5 depict time-out sequences.

Since the time-outs occur from the POR pulse, if MCLR

is kept low long enough, the time-outs will expire. Then,

bringing MCLR high will begin execution immediately

(see Figure 14-4). This is useful for testing purposes or

to synchronize more than one MCP19111 device

operating in parallel.

14.6.1

POWER CONTROL (PCON)

The Power Control register PCON (address 8Eh) has

two Status bits to indicate what type of Reset occurred

last.

FIGURE 14-3:

TIME-OUT SEQUENCE ON POWER-UP (DELAYED MCLR): CASE 1

Note:

Voltage spikes below VSS at the MCLR

pin, inducing currents greater than 80 mA,

may cause latch-up. Thus, a series resis-

tor of 50-100 should be used when

applying a “low” level to the MCLR pin,

rather than pulling this pin directly to VSS.

TPWRT

TIOSCST

VDD

MCLR

Internal POR

PWRT Time-out

OST Time-out

Internal Reset

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