MMC2107 - Freescale Semiconductor

Freescale Semiconductor, Inc.
Serial Communications Interface Modules (SCI1 and SCI2)
Loop Operation
Enable single-wire operation by setting the LOOPS bit and the RSRC bit
in SCICR1. Setting the LOOPS bit disables the path from the RXD pin 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).
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Freescale Semiconductor, I
16.14 Loop Operation
The WOMS bit in the SCICR1 register configures the TXD pin for full
CMOS drive or for open-drain drive. WOMS controls the TXD pin in both
normal operation and in single-wire operation. When WOMS is set, the
DDR bit for the TXD pin does not have to be cleared for transmitter to
receive data.
In loop mode (LOOPS = 1, RSRC = 0), the transmitter output goes to the
receiver input. The RXD pin is disconnected from the SCI and is
available as a general-purpose I/O pin.
Setting the DDR bit for the TXD pin connects the transmitter output to the
TXD pin. Clearing the data direction bit disconnects the transmitter
output from the TXD pin.
TXD SCIDDR
BIT = 1
TXD SCIDDR
BIT = 0
TRANSMITTER
RECEIVER
TRANSMITTER
RECEIVER
H
WOMS
WOMS
TXD
RXD
TXD
RXD
GENERAL-PURPOSE I/O
GENERAL-PURPOSE I/O
Figure 16-26. Loop Operation (LOOPS = 1, RSRC = 0)
MMC2107 – Rev. 2.0
Technical Data
MOTOROLA Serial Communications Interface Modules (SCI1 and SCI2) 367
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