Chapter 20 Serial Communication Interface (S12SCIV5)
MC9S12XE-Family Reference Manual , Rev. 1.19
756
Freescale Semiconductor
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 RXD pin to the receiver. Setting
the RSRC bit connects the TXD pin to the receiver. 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.
NOTE
In single-wire operation data from the TXD pin is inverted if RXPOL is set.
20.4.8
Loop Operation
In loop operation the transmitter output goes to the receiver input. The RXD pin is disconnected from the
SCI.
Figure 20-31. 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 RXD pin 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).
NOTE
In loop operation data from the transmitter is not recognized by the receiver
if RXPOL and TXPOL are not the same.
20.5
Initialization/Application Information
20.5.1
Reset Initialization
See
Section 20.3.2, “Register Descriptions”
.
20.5.2
Modes of Operation
20.5.2.1
Run Mode
Normal mode of operation.
To initialize a SCI transmission, see
Section 20.4.5.2, “Character Transmission”
.
RXD
Transmitter
Receiver
TXD
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages
