Motorola DSP56301 - Manual (Page 240)

I/O Signals
8 -4 DSP56301 User’s Manual
However, at least one of the three signals must be selected as an SCI signal to release the SCI
from reset.
To enable SCI interrupts, program the SCI control registers before any of the SCI signals are
programmed as SCI functions. In this case, only one transmit interrupt can be generated
because the Transmit Data Register is empty. The timer and timer interrupt operate regardless
of how the SCI pins are configured, either as SCI or GPIO.
8.2.1 Receive Data (RXD)
This input signal receives byte-oriented serial data and transfers the data to the SCI receive
shift register. Asynchronous input data is sampled on the positive edge of the receive clock (1
×
SCLK ) if the SCI Clock Polarity (SCKP) bit is cleared. RXD can be configured as a GPIO
signal ( PE0 ) when the SCI RXD function is not in use.
8.2.2 Transmit Data (TXD)
This output signal transmits serial data from the SCI transmit shift register. Data changes on
the negative edge of the asynchronous transmit clock (
SCLK ) if SCKP is cleared. This output
is stable on the positive edge of the transmit clock. TXD can be programmed as a GPIO signal
( PE1 ) when the SCI TXD function is not in use.
8.2.3 SCI Serial Clock (SCLK)
This bidirectional signal provides an input or output clock from which the transmit and/or
receive baud rate is derived in Asynchronous mode and from which data is transferred in
Synchronous mode.
SCLK can be programmed as a GPIO signal ( PE2 ) when the SCI SCLK
function is not in use. This signal can be programmed as PE2 when data is being transmitted
on TXD , since the clock does not need to be transmitted in Asynchronous mode. Because
SCLK is independent of SCI data I/O, there is no connection between programming the PE2
signal as SCLK and data coming out the TXD signal.