Intel Microcontroller, 80C196NU, 8XC196NP manual 13.5.1 a 16-bit Example System

Models: Microcontroller 80C196NU 8XC196NP

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INTERFACING WITH EXTERNAL MEMORY

In multiplexed mode, with the full address on the bus for only half of the cycle, the external de- vice has less time to receive it and to respond. As a result, for the same bus-cycle length (4t) a multiplexed system requires a faster external device (unless wait states are added to the bus cy- cle). Although the multiplexed mode has this disadvantage, it is useful for compatibility with de- vices designed for multiplexed operation.

In a 16-bit system (left side of Figure 13-8 and Figure 13-9) one data word can be transferred over AD15:0 in a single bus cycle. In an 8-bit system, one data word is transferred as two bytes over AD7:0 in successive bus cycles, and AD15:8 drive the upper eight address bits for the entire bus cycle.

The flexibility of the chip-select unit enables you to specify the bus width, the number of wait states, and a multiplexed or demultiplexed bus for each of the six chip-select outputs. The system in Figure 13-5 on page 13-13 illustrates a mixture of 8-bit and 16-bit devices with different num- bers of wait states.

13.5.1 A 16-bit Example System

Figure 13-10 shows a 16-bit system in demultiplexed mode. The flash memory receives the ad- dress on A18:1; data is transferred on AD15:0. Using the WR# signal as shown, this system writes words and not single bytes to the memory. (Using WRL# and WRH#, you can write single bytes on a 16-bit bus.

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Intel Microcontroller, 80C196NU, 8XC196NP manual 13.5.1 a 16-bit Example System