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5.5.2 Processing of Specific Exceptions

The following paragraphs provide details concerning sources of specific exceptions, how each arises, and how each is processed.

5.5.2.1RESET. Assertion of RESET by external hardware or assertion of the internal RESET signal by an internal module causes a reset exception. The reset exception has the highest priority of any exception. Reset is used for system initialization and for recovery from catastrophic failure. The reset exception aborts any processing in progress when it is recognized, and that processing cannot be recovered. Reset performs the following operations:

1. Clears T0 and T1 in the SR to disable tracing

2.Sets the S-bit in the SR to establish supervisor privilege

3.Sets the interrupt priority mask to the highest priority level (%111)

4.Initializes the VBR to zero ($00000000)

5.Generates a vector number to reference the reset exception vector

6.Loads the first long word of the vector into the interrupt SP

7.Loads the second long word of the vector into the PC

8.Fetches and initiates decode of the first instruction to be executed

Figure 5-11 is a flowchart of the reset exception

After initial instruction prefetches, normal program execution begins at the address in the PC. The reset exception does not save the value of either the PC or the SR.

If a bus error or address error occurs during reset exception processing sequence, a double bus fault occurs, the processor halts, and the HALT signal is asserted to indicate the halted condition.

Execution of the RESET instruction does not cause a reset exception nor does it affect any internal CPU register. The SIM40 registers and the MCR in each internal peripheral module (DMA, timers, and serial modules) are not affected. All other internal peripheral module registers are reset the same as for a hardware reset. The external devices connected to the RESET signal are reset at the completion of the RESET instruction.

MOTOROLAMC68340 USER’S MANUAL5- 43

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MC68340 specifications

The Motorola MC68340 is a highly integrated microprocessor that was introduced in the early 1990s. It belongs to the 68000 family of microprocessors and is designed to cater to the demands of embedded systems, particularly in telecommunications and networking applications. This chip represents a significant evolution in microprocessor technology by combining a microprocessor core with additional peripherals on a single chip, making it an attractive solution for engineers looking to design compact and efficient systems.

One of the key features of the MC68340 is its 32-bit architecture, which allows for significant processing power and data handling capabilities. This architecture enables the processor to handle larger data sizes and perform more complex calculations compared to its 16-bit predecessors. The MC68340 operates at clock speeds typically ranging from 16 MHz to 25 MHz. Its dual instruction pipeline enhances throughput, allowing for simultaneous instruction fetches and executions, which significantly boosts performance.

A notable characteristic of the MC68340 is the inclusion of integrated peripherals, which help reduce the overall component count in a system. Key integrated components include a memory management unit (MMU), a direct memory access (DMA) controller, and various communication interfaces such as serial ports. The memory management capabilities enhance the processor's ability to manage memory resources efficiently, enabling it to support multitasking environments commonly found in modern computing.

In terms of connectivity, the MC68340 features connections for both synchronous and asynchronous serial communication, making it well-suited for networking tasks. The processor supports a range of bus standards, including address and data buses, which facilitate seamless interaction with peripheral devices.

Another important aspect of the MC68340 is its flexibility. The processor supports multiple operating modes, including multiple CPU configurations and compatibility with the Motorola 68000 family, allowing for easier integration into existing systems.

Moreover, the MC68340 boasts low power consumption compared to many of its contemporaries, making it an excellent choice for battery-operated applications, enhancing its appeal in sectors like telecommunications, industrial control, and automotive systems. Its combination of performance, integration, versatility, and efficiency has secured the MC68340 a reputable position in the annals of embedded systems technology, proving to be a valuable asset for developers and engineers alike.

Motorola MC68340 manual Freescale Semiconductor, Inc

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Figure 5-11 is a flowchart of the reset exception

After initial instruction prefetches, normal program execution begins at the address in the PC. The reset exception does not save the value of either the PC or the SR.

If a bus error or address error occurs during reset exception processing sequence, a double bus fault occurs, the processor halts, and the HALT signal is asserted to indicate the halted condition.

MC68340 specifications