Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 710

SCC HDLC Mode
23.12 SCC HDLC Status Register (SCCS)
The SCC status register (SCCS), shown in
on RXD. The real-time status of CTS and CD are part of the port C parallel I/O.
0
Field
Reset
R/W
Addr
Table 23-10 describes HDLC SCCS fields.
Bits Name
0–4 — Reserved, should be cleared.
5 FG Flags. The line is checked after the data has been decoded by the DPLL.
0 HDLC flags are not being received. The most recently received 8 bits are examined every bit time
to see if a flag is present.
1 HDLC flags are being received. FG is set as soon as an HDLC flag (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 flag 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.
23.13 SCC HDLC Programming Examples
The following sections show examples for programming an SCC in HDLC mode. The first example uses
an external clock. The second example implements Manchester encoding.
23.13.1 SCC HDLC Programming Example #1
The following initialization sequence is for an SCC HDLC channel with an external clock. SCC2 is used
with RTS2, CTS2, and CD2 active; CLK3 is used for both the HDLC receiver and transmitter.
1. Configure port A to enable TXD2 and RXD2. Set PAPAR[12,13] and clear PADIR[12,13] and
PAODR[12,13].
2. Configure port C to enable RTS2, CTS2, and CD2. Set PCPAR[14] and PCSO[8,9] and clear
PCPAR[8,9] and PCDIR[8,9,14].
23-14
Figure 23-9, permits monitoring of real-time status conditions
—
0000_0000
0xA37 (SCCS2), 0xA57 (SCCS3), 0xA77 (SCCS4)
Figure 23-9. SCC HDLC Status Register (SCCS)
Table 23-10. HDLC SCCS Field Descriptions
MPC885 PowerQUICC Family Reference Manual, Rev. 2
4 5
FG
R
Description
6 7
CS ID
Freescale Semiconductor