Motorola MPC823e Reference Manual page 623

CTSS—CTS Sampling
0 = The CTSx signal is assumed to be asynchronous with the data. It is internally
synchronized by a serial communication controller and data is then transmitted
after several serial clock delays.
1 = The CTSx signal is assumed to be synchronous with the data, which speeds up
operation. In this mode, CTSx must transition while the transmit clock is in the low
state. As soon as CTSx is low, data immediately begins transmission. This mode
is especially useful when connecting an MPC823e in transparent mode since it
allows the RTSx signal of one MPC823e to be directly connected to the CTSx
signal of another MPC823e.
TFL—Transmit FIFO Length
0 = Normal operation. The transmit FIFO is 32 bytes for each serial communication
controller.
1 = The transmit FIFO is 1 byte and can be used with character-oriented protocols to
ensure a minimum FIFO latency at the expense of performance.
RFW—Receive FIFO Width
0 = Receive FIFO is 32 bits wide for maximum performance. Data is not normally
written to receive buffers until at least 32 bits are received. This configuration is
required for HDLC-type protocols and Ethernet, but it is recommended for
high-performance transparent modes. In this mode, the receive FIFO is 32 bytes
for each serial communication controller.
1 = Low-latency operation. The receive FIFO is 8 bits wide and the receive FIFO is a
quarter its normal size (8 bytes). This allows data to be written to the data buffer
when a character is received, instead of waiting to receive 32 bits. This
configuration must be chosen for character-oriented protocols, such as UART. It
can also be used for low-performance, low-latency, transparent operation, if
preferred. However, when it is used with HDLC, HDLC Bus, AppleTalk, or Ethernet
modes, erratic behavior occurs.
TXSY—Transmitter Synchronized to the Receiver
This bit is specifically intended for X.21 applications in which the transmitted data must begin
an exact multiple of 8-bit periods after the received data arrives.
0 = No synchronization between receiver and transmitter (default).
1 = The transmit bitstream is synchronized to the receiver. Additionally, if the RSYN bit
is set to 1, then transmission in the totally transparent mode does not occur until
the receiver has synchronized with the bitstream and the CTSx signal is asserted
to a serial communication controller. Assuming CTSx is already asserted,
transmission begins eight clocks after the receiver starts receiving data.
MOTOROLA MPC823e REFERENCE MANUAL
Communication Processor Module
16-169