
392
10.5
SCI Interrupt Sources and the DMAC
The SCI has four interrupt sources: transmit-end (TEI), receive-error (ERI), receive-data-full
(RXI), and transmit-data-empty (TXI). Table 10.10 lists the interrupt sources and indicates their
priority. These interrupts may be enabled by setting the TIE, RIE, and TEIE bits in the serial
control register (SCR). Each interrupt request is sent independently to the interrupt controller.
TXI is requested when the TDRE bit in SCSR is set to 1. TXI can start the direct memory access
controller (DMAC) to transfer data. TDRE is automatically cleared to 0 when the DMAC executes
the data write to the transmit data register (SCTDR).
RXI is requested when the RDRF bit in SCSR is set to 1. RXI can start the DMAC to transfer
data. RDRF is automatically cleared to 0 when the DMAC executes the data read from the receive
data register (SCRDR).
When using the DMAC for the processing of TXI interrupt requests or RXI interrupt requests
instead of using the interrupt controller for that processing, make the priority ranking of interrupt
requests from the SCI low so that the interrupt controller will not operate.
ERI is requested when the ORER, PER, or FER bit in SCSR is set to 1. The DMAC is not
activated by ERI interrupt requests.
TEI is requested when the TEND bit in SCSR is set to 1. TEI cannot start the DMAC.
A TXI interrupt indicates that transmit data writing is enabled. A TEI interrupt indicates that the
transmit operation is completed.
Table 10.10 SCI Interrupt Sources
Interrupt Source
Description
DMAC Activation
Priority
ERIn
Interrupt due to receive error (ORER,
PER, or FER)
No
Highest
RXIn
Interrupt due to receive data full (RDRF) Yes
TXIn
Interrupt due to transmit data empty
(TDRE)
Yes
TEIn
Interrupt due to transmit end (TEND)
No
Lowest
Note:
n = 0, 1
10.6
Cautions on Use
Be careful of the following when using the SCI:
1. The relationship between writes to TDR and the TDRE flag: