MC68HC908AP16CFB datasheet(218/440 Pages) MOTOROLA

218 / 440 page

Serial Communications Interface

Data Sheet

MC68HC908AP Family — Rev. 2.5

218

MOTOROLA

13.4.2.1 Character Length

The transmitter can accommodate either 8-bit or 9-bit data. The state of

the M bit in SCI control register 1 (SCC1) determines character length.

When transmitting 9-bit data, bit T8 in SCI control register 3 (SCC3) is

the ninth bit (bit 8).

13.4.2.2 Character Transmission

During an SCI transmission, the transmit shift register shifts a character

out to the TxD pin. The SCI data register (SCDR) is the write-only buffer

between the internal data bus and the transmit shift register. To initiate

an SCI transmission:

1. Enable the SCI by writing a logic 1 to the enable SCI bit (ENSCI)

in SCI control register 1 (SCC1).

2. Enable the transmitter by writing a logic 1 to the transmitter enable

bit (TE) in SCI control register 2 (SCC2).

3. Clear the SCI transmitter empty bit by first reading SCI status

4. Repeat step 3 for each subsequent transmission.

At the start of a transmission, transmitter control logic automatically

loads the transmit shift register with a preamble of logic 1s. After the

preamble shifts out, control logic transfers the SCDR data into the

transmit shift register. A logic 0 start bit automatically goes into the least

significant bit position of the transmit shift register. A logic 1 stop bit goes

into the most significant bit position.

The SCI transmitter empty bit, SCTE, in SCS1 becomes set when the

SCDR transfers a byte to the transmit shift register. The SCTE bit

indicates that the SCDR can accept new data from the internal data bus.

If the SCI transmit interrupt enable bit, SCTIE, in SCC2 is also set, the

SCTE bit generates a transmitter CPU interrupt request.

When the transmit shift register is not transmitting a character, the TxD

pin goes to the idle condition, logic 1. If at any time software clears the

ENSCI bit in SCI control register 1 (SCC1), the transmitter and receiver

relinquish control of the port pin.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

MC68HC908AP16CFB Datasheet(PDF) 218 Page - Motorola, Inc