Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 748

SCC BISYNC Mode
26.11 BISYNC Mode Register (PSMR)
The PSMR is used as the BISYNC mode register, shown in
can be modified on the fly.
Bit
0
Field NOS
Reset
R/W
Addr
Figure 26-5. Protocol-Specific Mode Register for BISYNC (PSMR)
Table 26-10 describes PSMR fields.
Bits Name
0–3 NOS Minimum number of SYN1–SYN2 pairs (defined in DSR) sent between or before messages.If NOS
= 0000, one pair is sent. If NOS = 1111, 16 pairs are sent. The entire pair is always sent, regardless
of how GSMR[SYNL) is set. NOS can be modified on the fly.
4–5 CRC CRC selection
x0 Reserved.
01 CRC16 (BISYNC). X16 + X15 + X2 + 1. PRCRC and PTCRC should be initialized to all zeros or
all ones before the channel is enabled. In either case, the transmitter sends the calculated CRC
noninverted and the receiver checks the CRC against zero. Eight-bit data characters (without
parity) are configured when CRC16 is chosen.
11 LRC (sum check). (BISYNC). For even LRC, initialize PRCRC and PTCRC to zeros before the
channel is enabled; for odd LRC, they should be initialized to ones.
Note that the receiver checks character parity when BCS is programmed to LRC and the receiver
is not in transparent mode. The transmitter sends character parity when BCS is programmed to
LRC and the transmitter is not in transparent mode. Use of parity in BISYNC assumes that 7-bit
data characters are being used.
6 RBCS Receive BCS. The receiver internally stores two BCS calculations separated by an eight serial clock
delay to allow examination of a received byte to determine whether it should used in BCS
calculation.
0 Disable receive BCS.
1 Enable receive BCS. Should be set (or reset) within the time taken to receive the following data
byte. When RBCS is reset, BCS calculations exclude the latest fully received data byte. When
RBCS is set, BCS calculations continue as normal.
7 RTR Receiver transparent mode
0 Normal receiver mode with SYNC stripping and control character recognition.
1 Transparent receiver mode. SYNCs, DLEs, and control characters are recognized only after a
leading DLE character. The receiver calculates the CRC16 sequence even if it is programmed to
LRC while in transparent mode. Initialize PRCRC to the CRC16 preset value before setting RTR.
8 RVD Reverse data
0 Normal operation.
1 Any portion of the SCC defined to operate in BISYNC mode operates by reversing the character
bit order and sending the msb first.
26-10
3 4 5 6
CRC RBCS RTR RVD DRT
0xA28 (PSMR2), 0xA48 (PSMR3), 0xA68 (PSMR4)
Table 26-10. PSMR Field Descriptions
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Figure 26-5. PSMR[RBCS, RTR, RPM, TPM]
7 8 9 10 11
—
0
R/W
Description
12 13 14 15
RPM TPM
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