mc68hc908sr12 Freescale Semiconductor, Inc, mc68hc908sr12 Datasheet - Page 259

• Manufacturer Part Number: mc68hc908sr12
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

16.5.2.1 Character Length
16.5.2.2 Character Transmission
MC68HC908SR12•MC68HC08SR12 — Rev. 5.0
Freescale Semiconductor
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).
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:
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.
1. Enable the SCI by writing a logic 1 to the enable SCI bit (ENSCI)
2. Enable the transmitter by writing a logic 1 to the transmitter enable
3. Clear the SCI transmitter empty bit by first reading SCI status
4. Repeat step 3 for each subsequent transmission.
in SCI control register 1 (SCC1).
bit (TE) in SCI control register 2 (SCC2).
register 1 (SCS1) and then writing to the SCDR.
Serial Communications Interface (SCI)
Serial Communications Interface (SCI)
Functional Description
Data Sheet
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