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Communication Processor Module
16-196
MPC823 USER’S MANUAL
MOTOROLA
SCC2
COMMUNICATION
16
PROCESSOR
MODULE
All the standards provide handshaking signals, but some systems require just three physical
lines—transmit data, receive data, and ground. Many proprietary standards have been built
around the asynchronous character frame and some even implement a multidrop
configuration. In multidrop systems, more than two stations can be present on a network,
each one with a specific address. Frames made up of many characters can be broadcast
with the first character acting as a destination address. To accommodate this, the UART
frame is extended one bit to distinguish between an address character and the normal data
characters. Additionally, a synchronous form of the UART protocol exists where start and
stop bits are still present, but because a clock is provided with each bit the oversampling
technique is not required. This mode is called isochronous operation or synchronous UART.
By appropriately setting the GSMR_L, the SCC2 channel can be configured to function in
UART mode, which provides standard serial I/O using asynchronous character-oriented
(start-stop) protocols with RS-232 C-type lines. The SCC2 in UART mode, also called the
SCC2 UART controller, can be used to communicate with any existing RS-232 type of
device and to provide a port for serial communication to other microprocessors and
terminals (either locally or via modems). It includes facilities for communication using
standard asynchronous bit rates and protocols. The SCC2 in UART mode supports a
multidrop mode for master/slave operation with wake-up capability on both the idle signal
and address bit. This mode also supports a synchronous mode of operation where a clock
must be provided with each bit received. It transmits data from memory (either internal or
external) to the TXD2 signal and receives data from the RXD2 signal into memory. In
synchronous UART mode, the clock must also be supplied and it can be generated internally
or externally. Modem lines are supported via the port B and C pins. The SCC2 in UART
mode consists of separate transmit and receive sections whose operations are
asynchronous with the core.
16.9.15.1 FEATURES
The following list summarizes the main features of the SCC2 in UART mode:
Flexible message-oriented data structure
Implements synchronous and asynchronous UART
Multidrop operation
Receiver wake-up on idle line or address mode
Eight control character comparisons
Two address comparisons
Maintenance of four 16-bit error counters
Received break character length indication
Programmable data length (5–8 bits)
Programmable 1 to 2 stop bits in transmission
Capable of reception without a stop bit
Programmable fractional stop bit length
Even, odd, force, or no parity generation