MC9S12HZ256 Datasheet, PDF (416/692 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Chapter 13 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.
13.4.7 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 13-25. 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.
13.5 Interrupts
This section describes the interrupt originated by the SCI block.The MCU must service the interrupt
requests. Table 13-17 lists the five interrupt sources of the SCI.
Table 13-17. SCI Interrupt Sources
Interrupt
TDRE
Source
SCISR1[7]
TC
RDRF
SCISR1[6]
SCISR1[5]
OR
SCISR1[3]
Local Enable
TIE
TCIE
RIE
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.
MC9S12HZ256 Data Sheet, Rev. 2.04
416
Freescale Semiconductor