Motorola MPC8260 User Manual

21-14

MOTOROLA

The SCC status register (SCCS), shown in Figure 21-9, permits monitoring of real-time
status conditions on RXD. The real-time status of CTS and CD are part of the port C
parallel I/O.

The following sections show examples for programming SCCs in HDLC mode. The Þrst
example uses an external clock. The second example implements Manchester encoding.

Bit

0

1

2

3

4

5

6

7

Field

Ñ

FG

CS

ID

Reset

0000_0000

R/W

R

Addr

0x11A17 (SCCS1); 0x11A37 (SCCS2); 0x11A57 (SCCS3); 0x11A77 (SCCS4)

0Ð4

Ñ

Reserved, should be cleared.

5

FG

Flags. The line is checked after the data has been decoded by the DPLL.
0 HDLC ßags are not being received. The most recently received 8 bits are examined every bit time to 

see if a ßag is present. 

1 HDLC ßags are being received. FG is set as soon as an HDLC ßag (0x7E) is received on the line. 

Once it is set, it remains set at least 8 bit times and the next eight received bits are examined. If 
another ßag occurs, FG stays set for at least another eight bits. If not, it is cleared and the search 
begins again.

6

CS

Carrier sense (DPLL). Shows the real-time carrier sense of the line as determined by the DPLL. 
0 The DPLL does not sense a carrier.
1 The DPLL senses a carrier.

7

ID

Idle status. 
0 The line is busy.
1 Set when RXD is a logic 1 (idle) for 15 or more consecutive bit times. It is cleared after a single logic 

0 is received.