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
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Microcontroller, 80C196NU, 8XC196NP specifications

The Intel 8XC196NP and 80C196NU microcontrollers are part of Intel's renowned 16-bit microcontroller series that gained popularity in the 1980s and 1990s for embedded systems applications. Designed for a variety of applications, these microcontrollers are characterized by their robust performance, versatility, and industry-standard architecture.

The 8XC196NP features an enhanced instruction set with over 100 instructions, allowing for efficient code execution. It operates at clock speeds up to 16 MHz, which contributes to improved performance in time-sensitive applications. The microcontroller is equipped with a 16-bit data bus, enabling more efficient data handling compared to its 8-bit predecessors, thus accommodating complex algorithms and large data sets.

In terms of memory architecture, the 8XC196NP supports an addressable memory space of up to 64 KB of program memory and 64 KB of data memory. This configuration provides sufficient space for large applications while ensuring fast data access. The microcontroller includes integrated features such as timers, serial I/O capabilities, and interrupt processing, which enhance its functionality for real-time applications and control mechanisms.

The 80C196NU, on the other hand, is designed for lower power operation, making it suitable for battery-powered devices. This microcontroller maintains similar features to the 8XC196NP while offering advancements that support low-power consumption. The 80C196NU can also function in a range of temperature environments, making it adaptable for industrial applications.

Both the 8XC196NP and 80C196NU support external memory interfacing, allowing designers to expand the system's capability by connecting additional ROM and RAM. This flexibility makes them appealing for developing complex systems, such as motor controls, industrial automation, and consumer electronics.

Another standout feature of these microcontrollers is their built-in debugging capabilities. Intel provided hardware and software tools that enabled developers to test and troubleshoot their applications effectively, reducing the development time and increasing reliability.

Overall, the Intel 8XC196NP and 80C196NU microcontrollers stand out for their dependability, versatility, and performance, contributing significantly to the evolution of embedded system design. Their legacy continues to influence modern microcontroller technology, ensuring their relevance in a wide array of applications today.
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