Motorola DSP56309 User Manual page 233

Serial Communication Interface (SCI)
Operating Modes
The multidrop asynchronous modes are compatible with the MC68681 DUART, the
M68HC11 SCI interface, and the Intel 8051 serial interface.
8.4.1 SCI After Reset
There are four different methods of resetting the SCI.
1. Hardware RESET signal
2. Software RESET instruction:
Both hardware and software resets clear the port control register bits, which
configure all I/O as GPIO input. The SCI remains in the reset state as long as all
SCI signals are programmed as GPIO (PC2, PC1, and PC0 all are cleared); the SCI
becomes active only when at least one of the SCI I/O signals is not programmed
as GPIO.
3. Individual reset:
During program execution, the PC2, PC1, and PC0 bits can be cleared (individual
reset), which causes the SCI to stop serial activity and enter the reset state. All SCI
status bits are set to their reset state. However, the contents of the SCR are not
affected, allowing the DSP program to reset the SCI separately from the other
internal peripherals. During individual reset, internal DMA accesses to the data
registers of the SCI are not valid and the data read is unknown.
4. Stop processing state reset:
Executing the STOP instruction halts operation of the SCI until the DSP is
restarted, causing the SSR to be reset. No other SCI registers are affected by the
STOP instruction.
Table 8-3 on page 8-23 illustrates how each type of reset affects each register in the SCI.
8-22 DSP56309UM/D MOTOROLA