Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

Read and write bus cycles are distinguished by the RW bit. Read bus cycles will set this bit, and write bus cycles will clear it. RW is reloaded into the bus controller if the RR bit is set during unstacking.

0 = Faulted cycle was an operand write

1 = Faulted cycle was a prefetch or operand read

The LG bit indicates an original operand size of long word. LG is cleared if the original operand was a byte or word—SIZ will indicate original (and remaining) size. LG is set if the original was a long word—SIZ will indicate the remaining size at the time of fault. LG is ignored during unstacking.

0 = Original operand size was byte or word

1 = Original operand size was long word

The SSW SIZ field shows operand size remaining when a fault was detected. This field does not indicate the initial size of the operand, nor does it necessarily indicate the proper status of a dynamically sized bus cycle. Dynamic sizing occurs on the external bus and is transparent to the CPU. Byte size is shown only when the original operand was a byte. The field is reloaded into the bus controller if the RR bit is set during unstacking. The SIZ field is encoded as follows:

00—Long word 01—Byte 10—Word 11—Unused, reserved

The function code for the faulted cycle is stacked in the FUNC field of the SSW, which is a copy of FC2–FC0 for the faulted bus cycle. This field is reloaded into the bus controller if the RR bit is set during unstacking. All unused bits are stacked as zeros and are ignored during unstacking. Further discussion of the SSW is included in 5.5.3.1 Types of Faults.

5.5.3.1TYPES OF FAULTS. An efficient implementation of instruction restart dictates that faults on some bus cycles be treated differently than faults on other bus cycles. The CPU32 defines four fault types: released write faults, faults during exception processing, faults during MOVEM operand transfer, and faults on any other bus cycle.

5.5.3.1.1 Type I—Released Write Faults. CPU32 instruction pipelining can cause a final instruction write to overlap the execution of a following instruction. A write that is overlapped is called a released write. A released write fault occurs when a bus error or some other fault occurs on the released write.

Released write faults are taken at the next instruction boundary. The stacked PC is that of the next unexecuted instruction. If a subsequent instruction attempts an operand access while a released write fault is pending, the instruction is aborted and the write fault is acknowledged. This action prevents stale data from being used by the instruction.

5- 54MC68340 USER’S MANUALMOTOROLA

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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.
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