SCC HDLC Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor
22-7
22.8
HDLC Mode Register (PSMR)
The protocol-specific mode register (PSMR), shown in
Figure 22-3
, functions as the HDLC mode register.
Table 22-6
describes PSMR HDLC fields.
0
3
4
5
6
7
8
9
10
11
12
13
15
Field
NOF
CRC
RTE
—
FSE
DRT
BUS BRM MFF
—
Reset
0
R/W
R/W
Addr
0x0x11A08 (PSMR1); 0x0x11A28 (PSMR2); 0x0x11A48 (PSMR3); 0x0x11A68 (PSMR4)
Figure 22-3. HDLC Mode Register (PSMR)
Table 22-6. PSMR HDLC Field Descriptions
Bits
Name
Description
0-3
NOF
Number of flags. Minimum number of flags between or before frames. If NOF = 0b0000, no flags are
inserted between frames and the closing flag of one frame is followed by the opening flag of the next
frame in the case of back-to-back frames. NOF can be modified on-the-fly.
4–5
CRC
CRC selection.
00 16-bit CCITT-CRC (HDLC). X16 + X12 + X5 + 1.
x1 Reserved.
10 32-bit CCITT-CRC (Ethernet and HDLC). X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 +
X8 + X7 + X5 + X4 + X2 + X1 +1.
6
RTE
Retransmit enable.
0 No retransmission.
1 Automatic frame retransmission is enabled. Particularly useful in the HDLC bus protocol and
ISDN applications where multiple HDLC controllers can collide. Note that retransmission occurs
only if a lost CTS occurs on the first or second buffer of the frame.
7
—
Reserved, should be cleared.
8
FSE
Flag sharing enable. FSE can be set only if GSMR_H[RTSM] is already set. Can be modified
on-the-fly.
0 Normal operation.
1 If NOF[0–3] = 0b0000, a single shared flag is sent between back-to-back frames. Other values of
NOF[0–3] are decremented by 1. Useful in signaling system #7 applications.
9
DRT
Disable receiver while transmitting.
0 Normal operation.
1 As the SCC sends data, the receiver is disabled and gated by the internal RTS. This helps if the
HDLC channel is on a multidrop line and the SCC does not need to receive its own transmission.
Note:
If DRT = 1, GSMR_H[CDS] should be cleared unless both of the following are true: the same
clock is used for TCLK and RCLK, and CTS either has synchronous timing or is always
asserted.
10
BUS
HDLC bus mode.
0 Normal HDLC operation.
1 HDLC bus operation is selected. See
Section 22.15, “HDLC Bus Mode with Collision Detection
.”
Содержание MPC8250
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