Motorola PowerQUICC II MPC8280 Series Reference Manual page 733

RCLK
RXD
(Input)
CD
(Input)
NOTE:
1. GSMR_H[CDS] = 0. CDP=0.
2. If CD is negated prior to the last bit of the receive frame, CD lost is signaled in the frame BD.
3. If CDP=1, CD lost cannot occur and CD negation has no effect on reception.
RCLK
RXD
(Input)
CD
(Input)
Notes:
1. GSMR_H[CDS] = 1. CDP=0.
2. If CD is negated prior to the last bit of the receive frame, CD lost is signaled in the frame BD.
3. If CDP=1, CD lost cannot occur and CD negation has no effect on reception.
Figure 20-12. Using CD to Control Synchronous Protocol Reception
If CD is programmed to envelope the data, it must remain asserted during frame
transmission or a CD lost error occurs. Negation of CD terminates reception. If
GSMR_H[CDS] is zero, CD must be sampled by the SCC before a CD lost error is
recognized; otherwise, the negation of CD immediately causes the CD lost condition.
If GSMR_H[CDS] is set, all CD transitions must occur while the Rx clock is low.
20.3.5.2 Asynchronous Protocols
In asynchronous protocols, RTS is asserted when SCC data is loaded into the Tx FIFO and
a falling Tx clock occurs. CD and CTS can be used to control reception and transmission
in the same manner as the synchronous protocols. The first bit sent in an asynchronous
protocol is the start bit of the first character. In addition, the UART protocol has an option
for CTS flow control as described in Chapter 21, "SCC UART Mode."
• If CTS is already asserted when RTS is asserted, transmission begins in two
additional bit times.
• If CTS is not already asserted when RTS is asserted and GSMR_H[CTSS] = 0,
transmission begins in three additional bit times.
MOTOROLA Chapter 20. Serial Communications Controllers (SCCs)
Freescale Semiconductor, Inc.
First Bit of Frame Data
CD Sampled Low Here
First Bit of Frame Data
CD Assertion Immediately
Gates Reception
For More Information On This Product,
Go to: www.freescale.com
Last Bit of Frame Data
CD Sampled High Here
Last Bit of Frame Data
CD Negation Immediately
Halts Reception
SCC Parameter RAM
20-21