DSP56303 FREESCALE [Freescale Semiconductor, Inc], DSP56303 Datasheet - Page 180

• Manufacturer Part Number: DSP56303
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Serial Communication Interface (SCI)
8-12
Number
Bit
12
11
10
9
Name
ILIE
RIE
TIE
Bit
TE
Table 8-2. SCI Control Register (SCR) Bit Definitions (Continued)
Reset
Value
0
0
0
0
SCI Transmit Interrupt Enable
Enables/disables the SCI transmit data interrupt. If TIE is cleared, transmit data
interrupts are disabled, and the transmit data register empty (TDRE) bit in the SCI status
register must be polled to determine whether the transmit data register is empty. If both
TIE and TDRE are set, the SCI requests an SCI transmit data interrupt from the interrupt
controller. Either a hardware RESET signal or a software RESET instruction clears TIE.
SCI Receive Interrupt Enable
Enables/disables the SCI receive data interrupt. If RIE is cleared, the receive data
interrupt is disabled, and the RDRF bit in the SCI status register must be polled to
determine whether the receive data register is full. If both RIE and RDRF are set, the SCI
requests an SCI receive data interrupt from the interrupt controller. Receive interrupts
with exception have higher priority than normal receive data interrupts. Therefore, if an
exception occurs (that is, if PE, FE, or OR are set) and REIE is set, the SCI requests an
SCI receive data with exception interrupt from the interrupt controller. Either a hardware
RESET signal or a software RESET instruction clears RIE.
Idle Line Interrupt Enable
When ILIE is set, the SCI interrupt occurs when IDLE (SCI status register bit 3) is set.
When ILIE is cleared, the IDLE interrupt is disabled. Either a hardware RESET signal or
a software RESET instruction clears ILIE. An internal flag, the shift register idle interrupt
(SRIINT) flag, is the interrupt request to the interrupt controller. SRIINT is not directly
accessible to the user. When a valid start bit is received, an idle interrupt is generated if
both IDLE and ILIE are set. The idle interrupt acknowledge from the interrupt controller
clears this interrupt request. The idle interrupt is not asserted again until at least one
character has been received. The results are as follows:
• The IDLE bit shows the real status of the receive line at all times.
• An idle interrupt is generated once for each idle state, no matter how long the idle state
Transmitter Enable
When TE is set, the transmitter is enabled. When TE is cleared, the transmitter
completes transmission of data in the SCI transmit data shift register, and then the serial
output is forced high (that is, idle). Data present in the SCI transmit data register (STX) is
not transmitted. STX can be written and TDRE cleared, but the data is not transferred
into the shift register. TE does not inhibit TDRE or transmit interrupts. Either a hardware
RESET signal or a software RESET instruction clears TE.
Setting TE causes the transmitter to send a preamble of 10 or 11 consecutive ones
(depending on WDS), giving you a convenient way to ensure that the line goes idle
before a new message starts. To force this separation of messages by the minimum idle
line time, we recommend the following sequence:
If the first byte of the second message is not transferred to STX prior to the finish of the
preamble transmission, the transmit data line remains idle until STX is finally written.
lasts.
1.
2.
3.
4.
DSP56303 User’s Manual, Rev. 2
Write the last byte of the first message to STX.
Wait for TDRE to go high, indicating the last byte has been transferred to the
transmit shift register.
Clear TE and set TE to queue an idle line preamble to follow immediately the
transmission of the last character of the message (including the stop bit).
Write the first byte of the second message to STX.
Description
Freescale Semiconductor