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Synchronous Serial Interface

Table 8-5. Frame Sync and Clock Pin Configuration

SYN

RXD

TXD

SRFS

STFS

SRCK

STCK

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

0

0

RFS in

TFS in

RCK in

TCK in

 

 

 

 

 

 

 

0

0

1

RFS in

TFS out

RCK in

TCK out

 

 

 

 

 

 

 

0

1

0

RFS out

TFS in

RCK out

TCK in

 

 

 

 

 

 

 

0

1

1

RFS out

TFS out

RCK out

TCK out

 

 

 

 

 

 

 

1

0

0

GPIO

FS in

GPIO

CK in

 

 

 

 

 

 

 

1

0

1

GPIO

FS out

GPIO

CK out

 

 

 

 

 

 

 

1

1

0

GPIO

GPIO

GPIO

Gated in

 

 

 

 

 

 

 

1

1

1

GPIO

GPIO

GPIO

Gated out

 

 

 

 

 

 

 

8.2.8.8 Transmit Direction (TXD)—Bit 8

The transmit direction (TXD) control bit selects the direction and source of the clock and frame sync signals used to clock the TXSR. When the TXD bit is set, the frame sync and clock are generated internally and are output to the STFS and STCK pins, respectively, if not configured as GPIO. When the TXD bit is cleared, the clock source is external, the internal clock generator is disconnected from the STCK pin, and an external clock source can drive this pin to clock the TXSR. The STFS pin is an input, meaning that the transmit frame sync is supplied from an external source.

8.2.8.9 Synchronous Mode (SYN)—Bit 7

The synchronous mode (SYN) control bit enables the synchronous mode of operation. In this mode, the transmit and receive sections share a common clock pin (STCK) and frame sync pin (STFS).

8.2.8.10 Transmit Shift Direction (TSHFD)—Bit 6

The transmit shift direction (TSHFD) control bit controls whether the MSB or LSB is transmitted first for the transmit section. If the TSHFD bit is set, the LSB is transmitted first. If the TSHFD bit is cleared, the data is transmitted MSB first.

NOTE:

The codec device labels the MSB as bit 0, whereas the DSP56824 labels the LSB as bit 0. Therefore, when using a standard codec, the DSP56824 MSB (or codec bit 0) is shifted out first, and the TSHFD bit should be cleared.

8.2.8.11 Transmit Clock Polarity (TSCKP)—Bit 5

The transmit clock polarity (TSCKP) control bit controls which bit clock edge is used to clock out data and latch in data for the transmit section. If the TSCKP bit is set, the falling edge of the bit clock is used to clock the data out. If the TSCKP bit is cleared, the data is clocked out on the rising edge of the bit clock.

8-14

DSP56824 User’s Manual

 

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