MC68HC08AZ0 Datasheet, PDF (187/444 Pages) Motorola, Inc – Advance Information

Freescale Semiconductor, Inc.
Serial Communications Interface Module (SCI)
Functional description
Character transmission
During an SCI transmission, the transmit shift register shifts a
character out to the PTE0/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 ‘1’ to the enable SCI bit
(ENSCI) in SCI control register 1 (SCC1).
2. Enable the transmitter by writing a ‘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 register 1 (SCS1) and then writing to the SCDR.
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 ‘1’s. After the
preamble shifts out, control logic transfers the SCDR data into the
transmit shift register. A ‘0’ start bit automatically goes into the least
significant bit position of the transmit shift register. A ‘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 or a
transmitter DMA service request.
The SCTE bit generates a transmitter DMA service request if the DMA
transfer enable bit, DMATE, in SCI control register 3 (SCC3) is set.
Setting the DMATE bit enables the SCTE bit to generate transmitter
DMA service requests and disables transmitter CPU interrupt
requests.
When the transmit shift register is not transmitting a character, the
PTE0/TxD pin goes to the idle condition, ‘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 E pins.
7-sci
MOTOROLA
Serial Communications Interface Module (SCI)
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MC68HC08AZ0
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