DSP56303 datasheet(180/292 Pages) FREESCALE

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DSP56303 User’s Manual, Rev. 2

8-12

Freescale Semiconductor

Serial Communication Interface (SCI)

TIE

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

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.

RIE

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.

ILIE

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

lasts.

9TE

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:

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.

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.

Table 8-2. SCI Control Register (SCR) Bit Definitions (Continued)

Bit

Number

Bit

Name

Reset

Value

Description

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