ST90135 datasheet(163/190 Pages) STMICROELECTRONICS

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ST90158 - SERIAL COMMUNICATIONS INTERFACE (SCI)

SERIAL COMMUNICATIONS INTERFACE (Cont’d)

CLOCK CONFIGURATION REGISTER (CCR)

R251 - Read/Write

Reset value: 0000 0000 (00h)

Bit 7 = XTCLK

This bit, together with the OCLK bit, selects the

source for the transmitter clock. The following ta-

ble shows the coding of XTCLK and OCLK.

Bit 6 = OCLK

This bit, together with the XTCLK bit, selects the

source for the transmitter clock. The following ta-

ble shows the coding of XTCLK and OCLK.

Bit 5 = XRX:

External Receiver Clock Source.

0: External receiver clock source not used.

1: Select the external receiver clock source.

Note: The external receiver clock frequency must

be 16 times the data rate, or equal to the data rate,

depending on the status of the CD bit.

Bit 4 = XBRG:

Baud Rate Generator Clock

Source.

0: Select INTCLK for the baud rate generator.

1: Select the external receiver clock for the baud

rate generator.

Bit 3 = CD:

Clock Divisor.

The status of CD will determine the SCI configura-

tion (synchronous/asynchronous).

0: Select 16X clock mode for both receiver and

transmitter.

1: Select 1X clock mode for both receiver and

transmitter.

Note: In 1X clock mode, the transmitter will trans-

mit data at one data bit per clock period. In 16X

mode each data bit period will be 16 clock periods

long.

Bit 2 = AEN:

Auto Echo Enable.

0: No auto echo mode.

1: Put the SCI in auto echo mode.

Note: Auto Echo mode has the following effect:

the SCI transmitter is disconnected from the data-

out pin SOUT, which is driven directly by the re-

ceiver data-in pin, SIN. The receiver remains con-

nected to SIN and is operational, unless loopback

mode is also selected.

Bit 1 = LBEN:

Loopback Enable.

0: No loopback mode.

1: Put the SCI in loopback mode.

Note: In this mode, the transmitter output is set to

a high level, the receiver input is disconnected,

and the output of the Transmitter Shift Register is

looped back into the Receiver Shift Register input.

All interrupt sources (transmitter and receiver) are

operational.

Bit 0 = STPEN:

Stick Parity Enable.

0: The transmitter and the receiver will follow the

parity of even parity bit EP in the CHCR register.

1: The transmitter and the receiver will use the op-

posite parity type selected by the even parity bit

EP in the CHCR register.

XTCLK

OCLK

XRX

XBRG

AEN

LBEN

STPE N

XTCLK

OCLK

Pin Fun ction

Pin is used as a general I/O

Pin = TXCLK (used as an input)

Pin = CLKOUT (outputs the Baud

Rate Generator clock)

Pin = CLKOUT (outputs the Serial

expansion and synchronous

mode clock)

SPEN

Parity (Transmitter &

Receiver)

0 (odd)

Odd

1 (even)

Even

0 (odd)

Even

1 (even)

Odd

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