Motorola MPC8260 User Manual

MOTOROLA

Chapter 19.  Serial Communications Controllers (SCCs)  

19-21

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.

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 Þrst bit sent in an asynchronous
protocol is the start bit of the Þrst character. In addition, the UART protocol has an option
for CTS ßow control as described in Chapter 20, ÒSCC UART Mode.Ó

¥

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. 

¥

If CTS is not already asserted when RTS is asserted and GSMR_H[CTSS] = 1, 
transmission begins in two additional bit times.

1.  GSMR_H[CDS] = 0. CDP=0.

RCLK

First Bit of Frame Data

NOTE:

CD Sampled Low Here

RCLK

CD Sampled High Here

Last Bit of Frame Data

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.

1.  GSMR_H[CDS] = 1. CDP=0.

NOTE

:

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.

Last Bit of Frame Data

First Bit of Frame Data

CD Assertion Immediately
Gates Reception

CD Negation Immediately

Halts Reception

RXD

(Input)

CD

(Input)

CD

(Input)

RXD

(Input)