Motorola DSP56301 - Manual (Page 243)

SCI Initialization
Serial Communication Interface (SCI) 8 -7
There are two workarounds for this issue:
n Enable an SCI pin other than SCLK .
n In 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:
n For 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).
n Data 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).
n Data is transmitted only after the transmitter is enabled (TE = 1), and after the
initialization sequence has been transmitted (depending on the operating mode).
8.4.1 Preamble, Break, and Data Transmission Priority
Two or three transmission commands can be set simultaneously:
n A preamble (TE is set.)
n A break (SBK is set or is cleared.)
n An indication that there is data for transmission (TDRE is cleared.)