Receive Data (Rxd); Transmit Data (Txd); Sci Serial Clock (Sclk); Sci After Reset - Freescale Semiconductor DSP56311 User Manual

Serial Communication Interface (SCI)

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 ×
if the SCI Clock Polarity (SCKP) bit is cleared.
when the SCI function is not in use.
RXD

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 (
on the positive edge of the transmit clock.
the SCI function is not in use.
TXD

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. can be programmed as a GPIO signal (
SCLK
This signal can be programmed as
does not need to be transmitted in Asynchronous mode. Because
I/O, there is no connection between programming the
signal.
TXD

8.3 SCI After Reset

There are several different ways to reset the SCI:
Hardware
RESET
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 (
when at least one of the SCI I/O signals is not programmed as GPIO.
Individual reset:
During program execution, the PC2, PC1, and PC0 bits can all be cleared (that is,
individually reset), causing 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 remain unaffected
so the DSP program can 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 is unknown.
Stop processing state reset (that is, the STOP instruction)
Executing the STOP instruction halts operation of the SCI until the DSP is restarted,
8-4
TXD
when data is being transmitted on
PE2
signal
, , and
PC2 PC1 PC0
DSP56311 User's Manual, Rev. 2
can be configured as a GPIO signal (
RXD
) if SCKP is cleared. This output is stable
SCLK
can be programmed as a GPIO signal (
) when the SCI
PE2
SCLK
signal as
PE2 SCLK
all are cleared); the SCI becomes active only
PE0
) when
PE1
function is not in use.
SCLK
, since the clock
TXD
is independent of SCI data
and data coming out the
Freescale Semiconductor
)
SCLK
)