
Communication Processor Module
16-162
MPC823 USER’S MANUAL
MOTOROLA
SCC2
COMMUNICATION
16
PROCESSOR
MODULE
TTX—Transparent Transmitter
The serial communication controller offers totally transparent operation. However, to
increase flexibility, totally transparent operation is not configured with the MODE field, but
with the TTX and TRX bits. This gives you the opportunity to implement unique applications,
such as configuring an SCC2 receiver to an HDLC and configuring a transmitter to a totally
transparent operation. To do this, set MODE = HDLC, TTX = 1, and TRX = 0.
0 = Normal operation.
1 = The transmitter operates in totally transparent mode, regardless of the protocol
selected for the receiver in the MODE field of the GSMR_L.
CDP—Carrier-Detect Pulse
This bit must be set if the serial communication controller is used in the time-slot assigner.
0 = Normal operation (envelope mode). The CD signal should envelope the frame.
Negating CD while receiving data causes a CD lost error.
1 = Pulse mode. Once the CD signal is asserted, synchronization has been achieved
and further transitions of CD have no effect on reception.
CTSP—CTS Pulse
0 = Normal operation (envelope mode). The CTS signal should envelope the frame.
Negating CTS while transmitting data causes a CTS lost error.
1 = Pulse mode. Once the CTS signal is asserted, synchronization has been achieved
and further transitions of CTS have no effect on transmission.
CDS—Carrier-Detect Sampling
0 = The CD signal is assumed to be asynchronous with the data. It is internally
synchronized by the serial communication controller and then data is received.
1 = The CD signal is assumed to be synchronous with the data, which speeds up
operation. In this mode, CD must transition while the receive clock is in the low
state. As soon as CD is low, data is received. This mode is especially useful when
connecting an MPC823 in transparent mode because it allows the RTS signal of
one MPC823 to be directly connected to the CD signal of another MPC823.
Note:
Full-duplex transparent operation for a serial communication controller is
obtained by setting both TTX and TRX. The serial communication controller
cannot operate with Ethernet on its receiver or while transparent operation is on
its transmitter. In other words, if the MODE field is set to Ethernet, then TTX must
equal TRX or erratic operation will occur.