Intel 8XC196NP, Microcontroller manual Once Mode, Reserved Test Modes 80C196NU only

8XC196NP, 80C196NU USER’S MANUAL

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.

C =	( 0.0125) ( 0.0002)	1 μ F
	-------------------------------------------------- =
1	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.

C1	× Vt		( 1.0 × 10– 10)	( 2.5)	1.25 μs
TDIS = ---------	I---------	=	-----------------0.0002---------------------	------------=

12.6 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.

Holding the ONCE signal high during the rising edge of RESET# causes the device to enter ONCE mode. The ONCE signal is latched when RESET# goes inactive. Internally, the ONCE pin is tied to a medium-strength pull-down. To prevent accidental entry into ONCE mode, connect the ONCE pin to VSS.

Exit ONCE mode by asserting the RESET# signal. Normal operations resume when RESET# goes high.

12.7 RESERVED TEST MODES (80C196NU ONLY)

For the 80C196NU only, holding PLLEN1 low while PLLEN2 is held high causes the device to enter an unsupported test mode. Table 12-3 shows the proper PLLEN1 and PLLEN2 connections for valid clock modes.

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