Добавил:
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз: Предмет: Файл:
8XC196Kx,8XC196Jx,87C196CA microcontroller family user's manual.1995.pdf
Скачиваний:
64
Добавлен:
23.08.2013
Размер:
3.97 Mб
Скачать

SPECIAL OPERATING MODES

For example, assume that the oscillator needs at least 12.5 ms to discharge (TDIS = 12.5 ms), Vt is 2.5 V, and the discharge current is 200 μA. The minimum C1 capacitor size is 1 μF.

0.0125 × 0.0002

C1 = ------------------------------------------ = 1 μ F 2.5

When using an external oscillator, the value of C1 can be very small, allowing rapid recovery from powerdown. For example, a 100 pF capacitor discharges in 1.25 μs.

T

 

C1

× Vt

1.0

× 1010 × 2.5

1.25 μ s

DIS

= ------------------

= ------------------------------------------- =

 

 

I

 

0.0002

 

 

 

 

 

 

14.5 ONCE MODE

On-circuit emulation (ONCE) mode isolates the device from other components in the system to allow printed-circuit-board testing or debugging with a clip-on emulator. During ONCE mode, all pins except XTAL1, XTAL2, VSS, and VCC are weakly pulled high or low. During ONCE mode, RESET# must be held high or the device will exit ONCE mode and enter the reset state. Tables in Appendix B list the reset states of the pins (see Table B-8 on page B-20 for the 8XC196Kx, Table B-9 on page B-21 for the 8XC196Jx, or Table B-10 on page B-22 for the 87C196CA).

14.5.1 Entering and Exiting ONCE Mode

Holding the ONCE# signal low during the rising edge of RESET# causes the device to enter ONCE mode. To prevent accidental entry into ONCE mode, we highly recommend configuring this pin as an output. If you choose to configure this pin as an input, always hold it high during reset and ensure that your system meets the VIH specification (see datasheet) to prevent inadvertent entry into ONCE mode. Table 14-3 shows the ONCE# pin multiplexing for each device in the 8XC196Kx, Jx, and CA product families.

Table 14-3. ONCE# Pin Alternate Functions

Device

ONCE# Alternate Functions

 

 

8XC196CA

P2.6/HLDA#

 

 

8XC196Jx

P2.6/HLDA#

 

 

8XC196KQ, KR

P5.4/SLPINT

 

 

8XC196KS, KT

P2.6/HLDA#

 

 

Exit ONCE mode by asserting the RESET# signal and allowing the ONCE# pin to float or be pulled high. Normal operations resume when RESET# goes high.

14-9

Соседние файлы в предмете Электротехника