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DSP56303 User’s Manual, Rev. 2

8-8

Freescale Semiconductor

Serial Communication Interface (SCI)

back as it is received. After both numbers are loaded, the program size is in A0 and the starting

address is in A1.

The program is then loaded one byte at a time, least significant byte first. After the program is

loaded, the operating mode is set to zero, the CCR is cleared, and the DSP begins execution with

the first instruction loaded.

8.5 Exceptions

The SCI can cause five different exceptions in the DSP, discussed here from the highest to the

lowest priority:

SCI receive data with exception status occurs when the receive data register is full with

a receiver error (parity, framing, or overrun error). To clear the pending interrupt, read

the SCI status register; then read SRX. Use a long interrupt service routine to handle the

error condition. This interrupt is enabled by SCR[16] (REIE).

SCI receive data occurs when the receive data register is full. Read SRX to clear the

pending interrupt. This error-free interrupt can use a fast interrupt service routine for

minimum overhead. This interrupt is enabled by SCR[11] (RIE).

SCI transmit data occurs when the transmit data register is empty. Write STX to clear

the pending interrupt. This error-free interrupt can use a fast interrupt service routine for

minimum overhead. This interrupt is enabled by SCR[12] (TIE).

SCI idle line occurs when the receive line enters the idle state (10 or 11 bits of ones).

This interrupt is latched and then automatically reset when the interrupt is accepted.

This interrupt is enabled by SCR[10] (ILIE).

SCI timer occurs when the baud rate counter reaches zero. This interrupt is

automatically reset when the interrupt is accepted. This interrupt is enabled by SCR[13]

(TMIE).

8.6 SCI Programming Model

The SCI programming model can be viewed as three types of registers:

Control

— SCI Control Register (SCR) in Figure 8-3

— SCI Clock Control Register (SCCR) in Figure 8-4

Status

— SCI Status Register (SSR) in Figure 8-3

Data transfer

— SCI Receive Data Registers (SRX) in Figure 8-7

— SCI Transmit Data Registers (STX) in Figure 8-7

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