CHAPTER 13 INTERFACING WITH EXTERNAL MEMORY

The device can interface with a variety of external memory devices. Six chip-selects can be indi- vidually programmed for bus width, the number of wait states, and a multiplexed or demulti- plexed address/data bus. Other features of the external memory interface include ready control for inserting additional wait states, a bus-hold protocol that enables external devices to take con- trol of the bus, and two write-control modes for writing words and bytes to memory. These fea- tures provide a great deal of flexibility when interfacing with external memory devices.

In addition to describing the signals and registers related to external memory, this chapter discuss- es the process of fetching the chip configuration bytes and configuring the external bus. It also provides examples of external memory configurations and chip-select setup.

13.1 INTERNAL AND EXTERNAL ADDRESSES

The address that external devices see is different from the address that the device generates inter- nally. Internally, the device has 24 address lines, but only the lower 20 address lines (A19:0) are implemented with external pins. The absence of the upper four address bits at the external pins causes different internal addresses to have the same external address. For example, the internal addresses FF2080H, 7F2080H, and 0F2080H all appear at the 20 external pins as F2080H. The upper nibble of the internal address has no effect on the external address.

The address seen by an external device also depends on the number of address lines that the ex- ternal system uses. If the address on the external pins (A19:0) is F2080H, and only A17:0 are con- nected to the external device, the external device sees 32080H. The upper four address lines (A19:16) are implemented by the EPORT. Table 13-1 shows how the external address depends on the number of EPORT lines used to address the external device.

Table 13-1. Example of Internal and External Addresses

EPORT Lines

 

Address on the

Address Seen by

Connected to the

Internal Address

Device Pins

External Device

External Device

 

 

 

 

 

 

 

 

A16

xF2080H

F2080H

12080H

 

 

 

 

A17:16

xF2080H

F2080H

32080H

 

 

 

 

A18:16

xF2080H

F2080H

72080H

 

 

 

 

A19:16

xF2080H

F2080H

F2080H

 

 

 

 

13-1

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Intel 80C196NU, 8XC196NP, Microcontroller manual Example of Internal and External Addresses
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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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