Sci Clock Control Register (Sccr) - Motorola DSP56305 User Manual

8.3.3

SCI Clock Control Register (SCCR)

The SCCR is a sixteen bit read/write register that used to select clock modes and baud
rates for the transmitter and receiver sections of the SCI interface. The control bits are
described in the following paragraphs. The SCCR is cleared by hardware reset. The basic
features of the clock generator (see Figure 8-6 and Figure 8-7) are:
• The SCI logic always uses a 16
×
2 internal clock in the Synchronous mode. The maximum internal clock
available to the SCI peripheral block is the oscillator frequency divided by 4. With
an 80 MHz DSP56305 processor, this gives a maximum data rate of 1.25 Mbps for
asynchronous data and 10.0 Mbps for synchronous data. These maximum rates
are the same for internally or externally supplied clocks.
×
• The 16 clock is necessary for the Asynchronous modes to synchronize the SCI to
the incoming data (see Figure 8-6).
• In the Asynchronous modes, the user must provide a 16
to use an external baud rate generator (i.e., SCLK input).
• In the Asynchronous modes, the user can select either 1
clock when using internal TX and RX clocks (TCM = 0 and RCM = 0).
• If SCKP = 0, the data transmitted on the TXD signal changes on the negative edge
×
of the 1 serial clock and is stable on the positive edge. If SCKP = 1, the data
changes on the positive edge and is stable on the negative edge.
• If SCKP = 0, the data received on the RXD signal is sampled on the positive edge
or if SCKP = 1, on the negative edge of the 1
• In the Asynchronous modes, the output clock is continuous.
• In the Synchronous mode, a 1
The maximum 1
• In the Synchronous mode, the clock is gated.
• In the Synchronous mode, the transmitter and receiver are synchronous with each
other.
MOTOROLA
×
internal clock in the Asynchronous modes and a
×
clock is used for the output or input baud rate.
×
clock is the crystal frequency divided by 8.
DSP56305 User's Manual
Serial Communication Interface (SCI)
SCI Programming Model
×
clock if the user wishes
× ×
or 16
×
serial clock.
for the output
8-17