MC3S12RG128 Datasheet, PDF (469/546 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 16 Serial Communications Interface (SCIV2) Block Description
16.4.5 Single-Wire Operation
Normally, the SCI uses two pins for transmitting and receiving. In single-wire operation, the RXD pin is
disconnected from the SCI. The SCI uses the TXD pin for both receiving and transmitting.
TRANSMITTER
Tx OUTPUT SIGNAL
Tx INPUT SIGNAL
RECEIVER
RXD
Figure 16-22. Single-Wire Operation (LOOPS = 1, RSRC = 1)
Enable single-wire operation by setting the LOOPS bit and the receiver source bit, RSRC, in SCI control
register 1 (SCICR1). Setting the LOOPS bit disables the path from the Rx Input signal to the receiver.
Setting the RSRC bit connects the receiver input to the output of the TXD pin driver. Both the transmitter
and receiver must be enabled (TE = 1 and RE = 1).The TXDIR bit (SCISR2[1]) determines whether the
TXD pin is going to be used as an input (TXDIR = 0) or an output (TXDIR = 1) in this mode of operation.
16.4.6 Loop Operation
In loop operation the transmitter output goes to the receiver input. The Rx Input signal is disconnected
from the SCI
.
TRANSMITTER
Tx OUTPUT SIGNAL
RECEIVER
RXD
Figure 16-23. Loop Operation (LOOPS = 1, RSRC = 0)
Enable loop operation by setting the LOOPS bit and clearing the RSRC bit in SCI control register 1
(SCICR1). Setting the LOOPS bit disables the path from the Rx Input signal to the receiver. Clearing the
RSRC bit connects the transmitter output to the receiver input. Both the transmitter and receiver must be
enabled (TE = 1 and RE = 1).
16.5 Initialization Information
16.5.1 Reset Initialization
The reset state of each individual bit is listed in Section 16.3, “Memory Map and Registers” which details
the registers and their bit fields. All special functions or modes which are initialized during or just
following reset are described within this section.
MC3S12RG128 Data Sheet, Rev. 1.05
Freescale Semiconductor
469