Motorola DSP56301 user manual Preamble, Break, and Data Transmission Priority

Models: DSP56301

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SCI Initialization

There are two workarounds for this issue:

νEnable an SCI pin other than SCLK.

νIn the next instruction, enable the remaining SCI pins, including the SCLK pin.

Following is an example of one way to initialize the SCI:

1.Ensure that the SCI is in its individual reset state (PCRE = $0).

2.Configure the control registers (SCR, SCCR) according to the operating mode, but do not enable transmitter (TE = 0) or receiver (RE = 0).

Note: It is now possible to set the interrupts enable bits that are used during the operation. No interrupt occurs yet.

3.Enable the SCI by setting the PCRE bits according to which signals are used during operation.

4.If transmit interrupt is not used, write data to the transmitter.

Note: If transmitter interrupt enable is set, an interrupt is issued and the interrupt handler should write data into the transmitter. The DMA channel services the SCI transmit request if it is programmed to service the SCI transmitter.

5.Enable transmitters (TE = 1) and receiver (RE = 1) according to use. Operation starts as follows:

νFor an internally-generated clock, the SCLK signal starts operation immediately after the SCI is enabled (Step 3 above) for Asynchronous modes. In Synchronous mode, the SCLK signal is active only while transmitting (that is, a gated clock).

νData is received only when the receiver is enabled (RE = 1) and after the occurrence of the SCI receive sequence on the RXD signal, as defined by the operating mode (that is, idle line sequence).

νData is transmitted only after the transmitter is enabled (TE = 1), and after the initialization sequence has been transmitted (depending on the operating mode).

8.4.1Preamble, Break, and Data Transmission Priority

Two or three transmission commands can be set simultaneously:

νA preamble (TE is set.)

νA break (SBK is set or is cleared.)

νAn indication that there is data for transmission (TDRE is cleared.)

Serial Communication Interface (SCI)

8-7

Page 243
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Motorola DSP56301 user manual Preamble, Break, and Data Transmission Priority