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Freescale Semiconductor, Inc.

ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005

Freescale Semiconductor, Inc.

Synchronous Serial Interface

ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005

SCR2 bits are described in Section 8.2.8.1, “Receive Interrupt Enable (RIE)—Bit 15,” through Section 8.2.8.16, “Early Frame Sync (EFS)—Bit 0.” See Figure 8-6 on page 8-7 for the programming model of the SCR2.

As with all on-chip peripheral interrupts for the DSP56824, the status register (SR—bits I[1:0 = 01) must first be set to enable maskable interrupts (interrupts of level IPL 0). Next, the CH6 bit (Bit 9) in the interrupt priority register (IPR) must be set to enable the interrupt. Finally, the interrupt can be enabled from within the SSI.

8.2.8.1 Receive Interrupt Enable (RIE)—Bit 15

The SSI receive interrupt enable (RIE) control bit allows interrupting the program controller. When the RIE bit is set, the program controller is interrupted when the SSI receive data register full (RDF) bit in the SCSR is set.

When the receive buffer is enabled, two values are available to be read. If it is not enabled, then one value can be read from the SRX register. If the RIE bit is cleared, this interrupt is disabled. However, the RDF bit still indicates the receive data register full condition. Reading the SRX register clears the RDF bit, thus clearing the pending interrupt.

Two receive data interrupts with separate interrupt vectors are available: receive data with exception status, and receive data without exception. Table 8-3 shows these vectors and the conditions under which these interrupts are generated.

Table 8-3. SSI Receive Data Interrupts

Interrupt

Vector

RIE

ROE

RDF

 

 

 

 

 

 

 

 

 

 

Receive data with exception status

$0020

1

1

1

 

 

 

 

 

Receive data (without exception)

$0022

1

0

1

 

 

 

 

 

8.2.8.2 Transmit Interrupt Enable (TIE)—Bit 14

The SSI transmit interrupt enable (TIE) control bit allows interrupting the program controller. When the TIE bit is set, the program controller is interrupted when the SSI transmit data register empty (TDE) flag in the SCSR is set.

When the transmit buffer is enabled, two values can be written to the SSI. If it is not enabled, then one value can be written to the STX register. When the TIE bit is cleared, this interrupt is disabled. However, the TDE bit always indicates the STX register empty condition, even when the transmitter is disabled by the transmit enable (TE) bit (in the SCR2). Writing data to the STX or STSR clears the TDE bit, thus clearing the interrupt.

Two transmit data interrupts with separate interrupt vectors are available: transmit data with exception status and transmit data without exceptions. Table 8-4 shows the conditions under which these interrupts are generated and lists the interrupt vectors.

Table 8-4. SSI Transmit Data Interrupts

Interrupt

Vector

TIE

TUE

TDE

 

 

 

 

 

 

 

 

 

 

Transmit data with exception status

$0024

1

1

1

 

 

 

 

 

Transmit data (without exception)

$0026

1

0

1

 

 

 

 

 

8-12 DSP56824 User’s Manual

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