MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor 21-31
message is not addressed can set its RWU bit and return to the standby state. The RWU bit remains set and
the receiver remains on standby until another address frame appears on the RXD signal.
The logic 1 msb of an address frame clears the receiver’s RWU bit before the stop bit is received and sets
the RDRF flag.
Address mark wake-up allows messages to contain idle characters but requires that the msb be reserved
for use in address frames.
NOTE
With the WAKE bit clear, setting the RWU bit after the RXD signal has been
idle can cause the receiver to wake-up immediately.
21.4.6 Single-Wire Operation
Normally, the eSCI uses two pins for transmitting and receiving. In single-wire operation, the RXD pin is
disconnected from the eSCI. The eSCI uses the TXD pin for both receiving and transmitting.
Figure 21-21. Single-Wire Operation (LOOPS = 1, RSRC = 1)
Enable single-wire operation by setting the LOOPS bit and the receiver source bit, RSRC, in eSCI control
register 1 (ESCIx_CR1). Setting the LOOPS bit disables the path from the RXD signal to the receiver.
Setting the RSRC bit connects the receiver input to the output of the TXD pin driver.
During reception, both the transmitter and receiver must be enabled (TE = 1 and RE = 1). The
SIU_PCR89[PA] and SIU_PCR91[PA] bits must be set to select the TXD function for the relevant eSCI
module, and the TXD pin should be set for open drain operation (SIU_PCRnn[ODE] = 1). Weak pull-up
may optionally be enabled if the external transmitting device is also open drain. See Section 6.3.1.12, “Pad
Configuration Registers (SIU_PCR)”.
During transmission, the transmitter must be enabled (TE=1); the receiver may be enabled or disabled. If
the receiver is enabled (RE=1), transmissions will be echoed back on the receiver. Set or clear open drain
output enable depending on desired operation.
Transmitter
Receiver
TXD
TXD Input Signal
TXD Output Signal
RXD
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