COP8SCR9KMT7 datasheet(22/80 Pages) NSC

22 / 80 page

10.0 Functional Description

(Continued)

RANDOM after RESET at power-on

T2CNTRL: CLEARED

T3CNTRL: CLEARED

HSTCR: CLEARED

ITMR: Cleared except Bit 6 (HSON) = 1

Accumulator, Timer 1, Timer 2 and Timer 3:

RANDOM after RESET

WKEN, WKEDG: CLEARED

WKPND: RANDOM

SP (Stack Pointer):

Initialized to RAM address 06F Hex

B and X Pointers:

UNAFFECTED after RESET with power already applied

RANDOM after RESET at power-on

S Register: CLEARED

RAM:

UNAFFECTED after RESET with power already applied

RANDOM after RESET at power-on

USART:

PSR, ENU, ENUR, ENUI: Cleared except the TBMT bit

which is set to one.

ISP CONTROL:

ISPADLO: CLEARED

ISPADHI: CLEARED

PGMTIM: PRESET TO VALUE FOR 10 MHz CKI

WATCHDOG (if enabled):

The device comes out of reset with both the WATCH-

DOG logic and the Clock Monitor detector armed, with

the WATCHDOG service window bits set and the

Clock Monitor bit set. The WATCHDOG and Clock

Monitor circuits are inhibited during reset. The

WATCHDOG service window bits being initialized high

default to the maximum WATCHDOG service window

of 64k T0 clock cycles. The Clock Monitor bit being

initialized high will cause a Clock Monitor error follow-

ing reset if the clock has not reached the minimum

specified frequency at the termination of reset. A Clock

Monitor error will cause an active low error output on

pin G1. This error output will continue until 16–32 T0

clock cycles following the clock frequency reaching the

minimum specified value, at which time the G1 output

will go high.

10.7.1 External Reset

The RESET input when pulled low initializes the device. The

RESET pin must be held low for a minimum of one instruc-

tion cycle to guarantee a valid reset. During Power-Up ini-

tialization, the user must ensure that the RESET pin of a

device without the Brownout Reset feature is held low until

the device is within the specified V

CC voltage. Any rising

edge on the RESET pin while V

CC is below the specified

operating range may cause unpredictable results. An R/C

circuit on the RESET pin with a delay 5 times (5x) greater

than the power supply rise time is recommended. Reset

should also be wide enough to ensure crystal start-up upon

Power-Up.

RESET may also be used to cause an exit from the HALT

mode.

A recommended reset circuit for this device is shown in

Figure 9.

10.7.2 On-Chip Brownout Reset

When enabled, the device generates an internal reset as

CC rises. While VCC is less than the specified brownout

voltage (V

bor), the device is held in the reset condition and

the Idle Timer is preset with 00Fx (240–256 t

C). When VCC

reaches a value greater than V

bor, the Idle Timer starts

counting down. Upon underflow of the Idle Timer, the internal

reset is released and the device will start executing instruc-

tions. This internal reset will perform the same functions as

external reset. Once V

CC is above the Vbor and this initial Idle

Timer time-out takes place, instruction execution begins and

the Idle Timer can be used normally. If, however, V

CC drops

below the selected V

bor, an internal reset is generated, and

the Idle Timer is preset with 00Fx. The device now waits until

CC is greater than Vbor and the countdown starts over.

When enabled, the functional operation of the device, at

frequency, is guaranteed down to the V

bor level.

One exception to the above is that the brownout circuit will

insert a delay of approximately 3 ms on power up or any time

the V

CC drops below a voltage of about 1.8V. The device will

be held in Reset for the duration of this delay before the Idle

Timer starts counting the 240 to 256 t

C. This delay starts as

soon as the V

CC rises above the trigger voltage (approxi-

mately 1.8V). This behavior is shown in Figure 10.

10138912

FIGURE 9. Reset Circuit Using External Reset

COP8SCR9KMT7 Folha de dados(PDF) 22 Page - National Semiconductor (TI)

COP8SCR9KMT7 Folha de dados(HTML) 22 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

Folha de dados Download

Ligação URL