DSP56857 datasheet(260/662 Pages) FREESCALE

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SCI Register Descriptions (SCI0_BASE = $1FFFE0 and SCI1_BASE = $1FFDF8)

5685X Digital Signal Controller User Manual, Rev. 4

10-24

Freescale Semiconductor

10.9.2.1 Loop Select Bit (LOOP)—Bit 15

This bit enables Loop operation. Loop operation disconnects the RXD pin from the SCI and the

transmitter output goes into the receiver input. Both the transmitter and receiver must be enabled

to use the internal Loop function as opposed to single wire operation, requiring only one or the

other to be enabled. Please see Table 10-11.

•

0 = Normal operation enabled

•

1 = Loop operation enabled

The receiver input is determined by the RSRC bit. The transmitter output is controlled by the TE

bit.

If the TE bit is set and LOOP = 1, the transmitter output appears on the TXD pin. If the TE bit is

clear and LOOP = 1, the TXD pin is high-impedance.

10.9.2.2 Stop in Wait Mode (SWAI)—Bit 14

This bit disables the SCI in the Wait mode.

•

0 = SCI enabled in Wait mode

•

1 = SCI disabled in Wait mode

10.9.2.3 Receiver Source (RSRC)— Bit 13

When LOOP = 1, the RSRC bit determines the internal feedback path for the receiver.

•

0 = Receiver input internally connected to transmitter output

•

1 = Receiver input connected to TXD pin

10.9.2.4 Data Format Mode (M)—Bit 12

This bit determines whether data characters are eight or nine bits long.

•

0 = One Start bit, eight data bits, one Stop bit

•

1 = One Start bit, nine data bits, one Stop bit

Table 10-11. Loop Functions

LOOP

RSRC

Function

Normal operation

Loop mode with internal TXD fed back to RXD

Single-wire mode with TXD output fed back to RXD

DSP56857 Datasheet(PDF) 260 Page - Freescale Semiconductor, Inc

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