SCC HDLC Mode
MPC885 PowerQUICC Family Reference Manual, Rev. 2
23-12
Freescale Semiconductor
The data length and buffer pointer fields are described in
Section 21.3, “SCC Buffer Descriptors (BDs).”
23.11 HDLC Event Register (SCCE)/HDLC Mask Register (SCCM)
The SCC event register (SCCE) is used as the HDLC event register to report events recognized by the
HDLC channel and to generate interrupts. When an event is recognized, the SCC sets the corresponding
SCCE bit. Interrupts generated through SCCE can be masked in the SCC mask register (SCCM) which has
the same bit format as the SCCE. Setting an SCCM bit enables the corresponding interrupt; clearing a bit
masks it. SCCE bits are cleared by writing ones; writing zeros has no effect. All unmasked bits must be
cleared before the CPM clears the internal interrupt request.
Figure 23-7
shows SCCE/SCCM for HDLC
operation.
Table 23-9
describes SCCE/SCCM fields.
0
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Field
—
GLR
GLT
DCC
FLG
IDL
GRA
—
TXE
RXF
BSY
TXB
RXB
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0xA30 (SCCE2)/0xA34 (SCCM2) 0xA50 (SCCE3)/0xA54 (SCCM3); 0xA70 (SCCE4)/0xA74 (SCCM4)
Figure 23-7. HDLC Event Register (SCCE)/HDLC Mask Register (SCCM)
Table 23-9. SCCE/SCCM Field Descriptions
Bits
Name
Description
0–2
—
Reserved, should be cleared.
3, 4
GLR/
GLT
Glitch on Rx/Tx. Set when the SCC detects a clock glitch on the receive/transmit clock. See
Section 21.4.6, “Clock Glitch Detection.”
5
DCC
DPLL carrier sense changed. Set when the carrier sense status generated by the DPLL changes.
Real-time status can be read in SCCS[CS]. This is not the CD status reported in port C. Valid only
when the DPLL is used.
6
FLG
Flag status. Set when the SCC stops or starts receiving HDLC flags. Real-time status can be read
in SCCS[FG].
7
IDL
Idle sequence status changed. Set when HDLC line status changes. Real-time status of the line can
be read in SCCS[ID].
8
GRA
Graceful stop complete. A
GRACEFUL
STOP
TRANSMIT
command completed execution. Set as soon
as the transmitter has sent a frame in progress when the command was issued. Set immediately if
no frame was in progress when the command was issued.
9–10
—
Reserved, should be cleared.
11
TXE
Tx error. Indicates an error (CTS lost or underrun) has occurred on the transmitter channel.
12
RXF
Rx frame. Set when the number of receive frames specified in RFTHR are received on the HDLC
channel. It is set no sooner than two clocks after the last bit of the closing flag is received. This event
is not maskable via the RxBD[I] bit.
13
BSY
Busy condition. Indicates a frame arrived but was discarded due to a lack of buffers.
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