MC9S12E256 Datasheet, PDF (272/602 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Chapter 8 Serial Communication Interface (SCIV4)
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.
8.4.7 Loop Operation
In loop operation the transmitter output goes to the receiver input. The RXD pin is disconnected from the
SCI
.
TRANSMITTER
TXD
RECEIVER
RXD
Figure 8-25. 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.
8.5 Interrupts
This section describes the interrupt originated by the SCI block.The MCU must service the interrupt
requests. Table 8-17 lists the five interrupt sources of the SCI.
Table 8-17. SCI Interrupt Sources
Interrupt
TDRE
TC
RDRF
OR
IDLE
Source
SCISR1[7]
SCISR1[6]
SCISR1[5]
SCISR1[3]
SCISR1[4]
Local Enable
TIE
TCIE
RIE
ILIE
Description
Active high level. Indicates that a byte was transferred from SCIDRH/L to
the transmit shift register.
Active high level. Indicates that a transmit is complete.
Active high level. The RDRF interrupt indicates that received data is
available in the SCI data register.
Active high level. This interrupt indicates that an overrun condition has
occurred.
Active high level. Indicates that receiver input has become idle.
MC9S12E256 Data Sheet, Rev. 1.08
272
Freescale Semiconductor