Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

7.3.3 Looping Modes

Each serial module channel can be configured to operate in various looping modes as shown in Figure 7-7. These modes are useful for local and remote system diagnostic functions. The modes are described in the following paragraphs with further information available in 7.4 Register Description and Programming.

The channel's transmitter and receiver should both be disabled when switching between modes. The selected mode is activated immediately upon mode selection, regardless of whether a character is being received or transmitted.

7.3.3.1AUTOMATIC ECHO MODE. In this mode, the channel automatically retransmits the received data on a bit-by-bit basis. The local CPU32-to-receiver communication continues normally, but the CPU32-to-transmitter link is disabled. While in this mode, received data is clocked on the receiver clock and retransmitted on TxDx. The receiver must be enabled, but the transmitter need not be enabled.

Since the transmitter is not active, the SR TxEMP and TxRDY bits are inactive, and data is transmitted as it is received. Received parity is checked, but not recalculated for transmission. Character framing is also checked, but stop bits are transmitted as received. A received break is echoed as received until the next valid start bit is detected.

7.3.3.2LOCAL LOOPBACK MODE. In this mode, TxDx is internally connected to RxDx. This mode is useful for testing the operation of a local serial module channel by sending data to the transmitter and checking data assembled by the receiver. In this manner, correct channel operations can be assured. Also, both transmitter and CPU32-to-receiver communications continue normally in this mode. While in this mode, the RxDx input data is ignored, the TxDx is held marking, and the receiver is clocked by the transmitter clock. The transmitter must be enabled, but the receiver need not be enabled.

7.3.3.3REMOTE LOOPBACK MODE. In this mode, the channel automatically transmits received data on the TxDx output on a bit-by-bit basis. The local CPU32-to-transmitter link is disabled. This mode is useful in testing receiver and transmitter operation of a remote channel. While in this mode, the receiver clock is used for the transmitter.

Since the receiver is not active, received data cannot be read by the CPU32, and the error status conditions are inactive. Received parity is not checked and is not recalculated for transmission. Stop bits are transmitted as received. A received break is echoed as received until the next valid start bit is detected.

7- 14MC68340 USER’S MANUALMOTOROLA

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Motorola MC68340 manual Freescale Semiconductor, Inc Looping Modes
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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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