barcode reader in asp.net Copyright 2008, 2002, 1997 by The McGraw-Hill Companies, Inc. Click here for terms of use. in Software

Creating QR Code ISO/IEC18004 in Software Copyright 2008, 2002, 1997 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Copyright 2008, 2002, 1997 by The McGraw-Hill Companies, Inc. Click here for terms of use.
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EMULATORS AND DEBUGGERS
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Figure 5.1 The most basic emulator consists of I/O functions that can be controlled by a PC.
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emulator that is controlled by a PC or workstation (see Fig. 5.1). In this type of emulator, simulator code in the PC runs the PIC microcontroller application and accesses the emulator pod s I/O pins. This type of emulator is very inexpensive, but probably is the least accurate of the three types in terms of timing and electrical behavior of the I/O pins. Using a PC with a PIII processor and a high speed interface, the actual speed of the application will be approximately the same as what the PIC microcontroller would produce although there would probably be some signi cant differences in edge to edge timing. The pin operation can be dif cult to properly simulate using discrete chips, but a CMOS PLD could be designed to accurately model the PIC microcontroller s pin behavior. This problem could be eliminated by writing a small PIC microcontroller application that allows a PC to interface with it and remotely control the operation of the I/O ports as is shown in Fig. 5.2. This emulator is the same type as the circuit presented later in this chapter (the Emu-II) and takes advantage of the PIC16F87x family of PIC microcontrollers, which can read and write internal program memory. The Emu-II uses this feature to load and execute code in the PIC microcontroller as is shown in Fig. 5.3. This type of emulator is often called a downloader and can be created quite inexpensively, but the limited program memory of the PIC microcontroller means that only relatively simple operations can be implemented.
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Figure 5.2 A PIC microcontroller can be used to provide the I/O pins required for an emulator controlled by an external PC.
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EMULATORS AND DEBUGGERS
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Figure 5.3 A PIC microcontroller executing the emulator functions by running the application code within its program memory and communicating with an external controller.
The emulator concept presented in Fig. 5.3 is extended to be built into many different PIC microcontroller devices that have ICD 2 debugger functionality built into them (Fig. 5.4). The 16F87x, PIC18, and many other PIC microcontroller part numbers have built-in serial port features that allow custom hardware to a synchronous serial port to access the different registers and functions of the PIC microcontroller via the MPLAB ICD 2 Puck, which provides a USB interface to the PC and a synchronous serial interface to the emulated (debugged) chip. As noted above, a selection of I/O pins (often MCLR#, RB3, RB6, and RB7) is required for the emulator functions and using these pins for this purpose reduces the total number of pins available to the application. For some devices, like the 18-pin parts, these pins are part of the only full 8-bit port available, which means that often the application cannot run the full, unchanged application with the ICD 2 debugger active. The last type of emulator is the most expensive, but it does address all the issues raised by the other methods that have been presented. Built into every PIC microcontroller chip are the I/O pins that can be used by external hardware to control the operation of the PIC microcontroller as well as provide a separate memory to execute out of. To provide access to these I/O pins, a special type of package (known as a bondout chip) is used. The bondout chip package is used to interface to the application and the emulator so that if any damaging voltages or currents are driven into the emulator by the application, this is the only part that has to be replaced. The cost for a bondout chip is on the order of $500, which, though expensive, is a lot cheaper than replacing a $2,000 emulator. The block for this type of emulator is shown in Fig. 5.5.
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