SCC UART Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
21-2 Freescale Semiconductor
In synchronous UART (isochronous operation), a separate clock signal is explicitly provided with the data.
Start and stop bits are present in synchronous UART, but oversampling is not required because the clock
is provided with each bit.
The general SCC mode register (GSMR) is used to configure an SCC channel to function in UART mode,
which provides standard serial I/O using asynchronous character-based (start-stop) protocols with
RS-232C-type lines. Using standard asynchronous bit rates and protocols, an SCC UART controller can
communicate with any existing RS-232-type device and provides a serial communications port to other
microprocessors and terminals (either locally or via modems). The independent transmit and receive
sections, whose operations are asynchronous with the core, send data from memory (either internal or
external) to TXD and receive data from RXD. The UART controller supports a multidrop mode for
master/slave operations with wake-up capability on both the idle signal and address bit. It also supports
synchronous operation where a clock (internal or external) must be provided with each bit received.
21.1 Features
The following list summarizes main features of an SCC UART controller:
Flexible message-based data structure
Implements synchronous and asynchronous UART
Multidrop operation
Receiver wake-up on idle line or address bit
Receive entire messages into buffers as indicated by receiver idle timeout or by control character
reception
Eight control character comparison
Two address comparison in multidrop configurations
Maintenance of four 16-bit error counters
Received break character length indication
Programmable data length (5–8 bits)
Programmable fractional stop bit lengths (from 9/16 to 2 bits) in transmission
Capable of reception without a stop bit
Even/odd/force/no parity generation and check
Frame error, noise error, break, and idle detection
Transmit preamble and break sequences
Freeze transmission option with low-latency stop
21.2 Normal Asynchronous Mode
In normal asynchronous mode, the receive shift register receives incoming data on RXDx. Control bits in
the UART mode register (PSMR) define the length and format of the UART character. Bits are received
in the following order:
1. Start bit
2. 5–8 data bits (lsb first)