Motorola DSP56301 - Manual (Page 248)

SCI Programming Model
8 -12 DSP56301 User’s Manual
8.6.1 SCI Control Register (SCR)
The SCR is a read/write register that controls the serial interface operation. Seventeen of its
24 bits are defined.
.
23 22 21 20 19 18 17 16
REIE
15 14 13 12 11 10 9 8
SCKP STIR TMIE TIE RIE ILIE TE RE
7 6 5 4 3 2 1 0
WOMS RWU WAKE SBK SSFTD WDS2 WDS1 WDS0
—Reserved bit; read as 0; write to 0 for future compatibility.
Figure 8-3. SCI Control Register (SCR)
Table 8-2. SCI Control Register (SCR) Bit Definitions
Bit
Number
Bit Name
Reset
Value
Description
23–17 0 Reserved. Write to 0 for future compatibility.
16 REIE 0 Receive with Exception Interrupt Enable
Enables/disables the SCI receive data with exception interrupt. If REIE is cleared, the
receive data with exception interrupt is disabled. If both REIE and RDRF are set, and
PE, FE, and OR are not all cleared, the SCI requests an SCI receive data with
exception interrupt from the interrupt controller. Either a hardware RESET signal or a
software RESET instruction clears REIE.
15 SCKP 0 SCI Clock Polarity
Controls the clock polarity sourced or received on the clock signal (SCLK), eliminating
the need for an external inverter. When SCKP is cleared, the clock polarity is positive;
when SCKP is set, the clock polarity is negative. In Synchronous mode, positive
polarity means that the clock is normally positive and transitions negative during valid
data. Negative polarity means that the clock is normally negative and transitions
positive during valid data. In Asynchronous mode, positive polarity means that the
rising edge of the clock occurs in the center of the period that data is valid. Negative
polarity means that the falling edge of the clock occurs during the center of the period
that data is valid. Either a hardware RESET signal or a software RESET instruction
clears SCKP.
14 STIR 0 Timer Interrupt Rate
Controls a divide-by-32 in the SCI Timer interrupt generator. When STIR is cleared, the
divide-by-32 is inserted in the chain. When STIR is set, the divide-by-32 is bypassed,
thereby increasing timer resolution by a factor of 32. Either a hardware RESET signal
or a software RESET instruction clears this bit. To ensure proper operation of the timer,
STIR must not be changed during timer operation (that is, if TMIE = 1).