Intel 8XC196NP, 80C196NU External Memory Interface Signals, Name Type Description Multiplexed

8XC196NP, 80C196NU USER’S MANUAL

13.2 EXTERNAL MEMORY INTERFACE SIGNALS

Table 13-2 describes the external memory interface signals. For some signals, the pin has an al- ternate function (shown in the Multiplexed With column). In some cases the alternate function is a port signal (e.g., P2.7). Chapter 7, “I/O Ports,” describes how to configure a pin for its I/O port function and for its special function. In other cases, the signal description includes instructions for selecting the alternate function.

Table 13-2. External Memory Interface Signals

Name	Type	Description	Multiplexed
			With
A15:0	I/O	System Address Bus	—
		These address lines provide address bits 15–0 during the entire
		external memory cycle during both multiplexed and demultiplexed
		bus modes.
A19:16	I/O	Address Lines 16–19	EPORT.3:0
		These address lines provide address bits 16–19 during the entire
		external memory cycle, supporting extended addressing of the
		1 Mbyte address space.
		NOTE: Internally, there are 24 address bits; however, only 20
		address lines (A19:0) are bonded out. The internal address
		space is 16 Mbytes (000000–FFFFFFH) and the external
		address space is 1 Mbyte (00000–FFFFFH). The device
		resets to FF2080H in internal ROM or F2080H in external
		memory.
AD15:0	I/O	Address/Data Lines	—
		The function of these pins depend on the bus size and mode. When
		a bus access is not occurring, these pins revert to their I/O port
		function.
		16-bit Multiplexed Bus Mode:
		AD15:0 drive address bits 0–15 during the first half of the bus cycle
		and drive or receive data during the second half of the bus cycle.
		8-bit Multiplexed Bus Mode:
		AD15:8 drive address bits 8–15 during the entire bus cycle. AD7:0
		drive address bits 0–7 during the first half of the bus cycle and either
		drive or receive data during the second half of the bus cycle.
		16-bit Demultiplexed Mode:
		AD15:0 drive or receive data during the entire bus cycle.
		8-bit Demultiplexed Mode:
		AD7:0 drive or receive data during the entire bus cycle. AD15:8 drive
		the data that is currently on the high byte of the internal bus.

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