HCS08 datasheet(175/290 Pages) MOTOROLA

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Data Sheet — MC9S08GB60/D V1.5

MOTOROLA

175

MC9S08GB/GT

Figure 11-3 SCI Transmitter Block Diagram

The transmitter is enabled by setting the TE bit in SCIxC2. This queues a preamble character which is one

full character frame of logic high. The transmitter then remains idle (TxD pin remains high) until data is

available in the transmit data buffer. Programs store data into the transmit data buffer by writing to the SCI

data register (SCIxD).

The central element of the SCI transmitter is the transmit shift register which is either 10 or 11 bits long

depending on the setting in the M control bit. For the remainder of this section, we will assume M = 0,

selecting the normal 8-bit data mode. In 8-bit data mode, the shift register holds a start bit, eight data bits,

and a stop bit. When the transmit shift register is available for a new SCI character, the value waiting in

the transmit data register is transferred to the shift register (synchronized with the baud rate clock) and the

transmit data register empty (TDRE) status flag is set to indicate another character may be written to the

transmit data buffer at SCIxD.

SCID – Tx BUFFER

(WRITE-ONLY)

INTERNAL BUS

11-BIT TRANSMIT SHIFT REGISTER

SHIFT DIRECTION

× BAUD

RATE CLOCK

PARITY

GENERATION

TRANSMIT CONTROL

ENABLE

SCI CONTROLS TxD

TxD DIRECTION

TO TxD

PIN LOGIC

LOOP

CONTROL

TO RECEIVE

DATA IN

TO TxD PIN

Tx INTERRUPT

REQUEST

LOOPS

RSRC

TIE

TDRE

TCIE

SBK

TXDIR

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