Intel Microcontroller, 80C196NU, 8XC196NP manual P2.7/CLKOUT

8XC196NP, 80C196NU USER’S MANUAL

P2.7/CLKOUT	Following reset, P2.7 carries the strongly driven CLKOUT signal. It
	is not held high. When P2.7 is configured as CLKOUT, it is always a
	complementary output.
P2.7	A value written to P2_REG.7 is held in a buffer until P2_MODE.7 is
	cleared, at which time the value is loaded into P2_REG.7. A value
	read from P2_REG.7 is the value currently in the register, not the
	value in the buffer. Therefore, any change to P2_REG.7 can be read
	only after P2_MODE.7 is cleared.
Port 3	After reset, your software must configure the device to match the
	external system. This is accomplished by writing appropriate config-
	uration data into P3_MODE. Writing to P3_MODE not only
	configures the pins but also turns off the transistor that weakly holds
	the pins high (Q4 in Figure 7-1 on page 7-5). For this reason, even if
	port 3 is to be used as it is configured at reset, you should still write
	data into P3_MODE.
P3.0/CS0#	P3.0/CS0# is weakly pulled high during reset. After reset, it defaults
	to the CS0# function. This chip-select signal detects address ranges
	that contain the CCBs and FF2080H (program start-up address). See
	Chapter 13, “Interfacing with External Memory,” for a detailed
	description of chip-select signal functions after reset.
P3.6/EXTINT2	Writing to P3_MODE.6 sets the EXTINT2 interrupt pending bit
	(INT_PEND1.5). After configuring the port pins, clear the interrupt
	pending registers before globally enabling interrupts. See “Design
	Considerations for External Interrupt Inputs” on page 7-11.
P3.7/EXTINT3	Writing to P3_MODE.7 sets the EXTINT3 interrupt pending bit
	(INT_PEND1.6). After configuring the port pins, clear the interrupt
	pending registers before globally enabling interrupts. See “Design
	Considerations for External Interrupt Inputs” on page 7-11.
Port 4	After reset, your software must configure the device to match the
	external system. This is accomplished by writing appropriate config-
	uration data into P4_MODE. Writing to P4_MODE not only
	configures the pins but also turns off the transistor that weakly holds
	the pins high (Q4 in Figure 7-1 on page 7-5). For this reason, even if
	port 4 is to be used as it is configured at reset, you should still write
	data into P4_MODE.

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