mc9s12q128 Freescale Semiconductor, Inc, mc9s12q128 Datasheet - Page 405

• Manufacturer Part Number: mc9s12q128
• Description: Hcs12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

13.4.5
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.
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.
13.4.6
In loop operation the transmitter output goes to the receiver input. The Rx Input signal is disconnected
from the SCI
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).
13.5
13.5.1
The reset state of each individual bit is listed in
the registers and their bit fields. All special functions or modes which are initialized during or just
following reset are described within this section.
Freescale Semiconductor
.
Initialization Information
Single-Wire Operation
Loop Operation
Reset Initialization
Figure 13-22. Single-Wire Operation (LOOPS = 1, RSRC = 1)
Figure 13-23. Loop Operation (LOOPS = 1, RSRC = 0)
TRANSMITTER
TRANSMITTER
RECEIVER
RECEIVER
Chapter 13 Serial Communications Interface (S12SCIV2) Block Description
MC9S12Q128
Section 13.3, “Memory Map and Registers”
Rev 1.09
Tx OUTPUT SIGNAL
Tx OUTPUT SIGNAL
Tx INPUT SIGNAL
RXD
RXD
which details
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