Motorola MCF5281, MCF5282 user manual Looping Modes, Automatic Echo Mode, Local Loop-Back Mode

Models: MCF5282 MCF5281

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Operation

23.5.3 Looping Modes

The UART can be configured to operate in various looping modes as shown in Figure 23-21.These modes are useful for local and remote system diagnostic functions. The modes are described in the following paragraphs and in Section 23.3, “Register Descriptions.”

The UART’s transmitter and receiver should 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.

23.5.3.1Automatic Echo Mode

In automatic echo mode, shown in Figure 23-22,the UART automatically resends received data bit by bit. The local CPU-to-receiver communication continues normally, but the CPU-to-transmitter link is disabled. In this mode, received data is clocked on the receiver clock and re-sent on UTXD. The receiver must be enabled, but the transmitter need not be.

CPU

 

 

 

Rx

 

 

 

 

 

 

 

URXDn Input

Disabled

 

Disabled

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tx

 

 

 

 

UTXDn Output

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 23-22. Automatic Echo

Because the transmitter is inactive, USRn[TxEMP,TxRDY] are inactive and data is sent as it is received. Received parity is checked but is not recalculated for transmission. Character framing is also checked, but stop bits are sent as they are received. A received break is echoed as received until the next valid start bit is detected.

23.5.3.2Local Loop-Back Mode

Figure 23-23shows how UTXDn and URXDn are internally connected in local loop-back mode. This mode is for testing the operation of a local UART module channel by sending data to the transmitter and checking data assembled by the receiver to ensure proper operations.

CPU

 

Rx

 

 

 

 

Disabled

 

URXDn Input

 

 

 

 

 

Disabled

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tx

 

 

 

 

 

UTXDn Output

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 23-23. Local Loop-Back

Features of this local loop-back mode are as follows:

Transmitter and CPU-to-receiver communications continue normally in this mode.

URXDn input data is ignored

MOTOROLA

Chapter 23. UART Modules

23-25

Page 499
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Motorola MCF5281, MCF5282 user manual Looping Modes, Automatic Echo Mode, Local Loop-Back Mode