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SCI Registers 2-8 SPRU051
2.4 SCI Baud-Select Registers (SCIHBAUD, SCILBAUD)
The values in SCIHBAUD and SCILBAUD specify the baud rate for the SCI.
Figure 2¨C3. Baud-Select MSbyte Register (SCIHBAUD) ¡ª Address 7052h
15 14 13 12 11 10 9 8
BAUD15 (MSB) BAUD14 BAUD13 BAUD12 BAUD11 BAUD10 BAUD9 BAUD8
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
Figure 2¨C4. Baud-Select LSbyte Register (SCILBAUD) ¡ª Address 7053h
7 6 5 4 3 2 1 0
BAUD7 BAUD6 BAUD5 BAUD4 BAUD3 BAUD2 BAUD1
BAUD0
(LSB)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
Legend: R = Read access, W = Write access, S = Set only, -0 = value after reset
Bit(s) Name Reset Description
15¨C0 BAUD15¨C
BAUD0
0 SCI 16-bit baud selection Registers SCIHBAUD (MSbyte) and SCILBAUD
(LSbyte) are concatenated to form a 16-bit baud value, BRR.
The internally-generated serial clock is determined by the low speed
peripheral clock (LSPCLK) signal and the two baud-select registers. The
SCI uses the 16-bit value of these registers to select one of 64K serial clock
rates for the communication modes.
The SCI baud rate is calculated using the following equation:
SCI Asynchronous Baud LSPCLK
(BRR 1) 8
= ¡Á +
Alternatively,
BRR LSPCLK
SCI Asynchronous Baud 8
1 = ¡Á ¨C
Note that the above formulas are applicable only when
1 ¡Ü BRR ¡Ü 65535. If BRR = 0, then
SCI Asynchronous Baud LSPCLK
16
=
Where: BRR = the 16-bit value (in decimal) in the baud-select registers.
3-23 eCAN Registers SPRU074
3.4 Bit-Timing Configuration Register (CANBTC)
The CANBTC register is used to configure the CAN node with the appropriate
network-timing parameters. This register must be programmed before using
the CAN module.
This register is write-protected in user mode and can only be written in
initialization mode. (See Section 3.6.1 on page 3-34.)
Note: Forbidden Configuration Values
To avoid unpredictable behavior of the CAN module, the CANBTC register
should never be programmed with values not allowed by the CAN protocol
specification and by the bit timing rules listed in Section 2.1.1.
Figure 3¨C21. CANBTC Register Bits
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Reserved BRP.7 BRP.6 BRP.5 BRP.4 BRP.3 BRP.2 BRP.1 BRP.0
R-x RWPI-0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Reserved SBG SJW SAM TSEG1 TSEG2
R-0 RWPI0 RWPI-0 RWPI0 RWPI-0 RWPI-0
Legend: RWPI = Read in all modes, write in privilege mode during initialization mode only, -n = Value after reset
Bit(s) Name Description
31:24 Reserved Reads are undefined and writes have no effect.
23:16 BRP.7:0 Baud rate prescaler. This register sets the prescaler for the baud rate settings.
The length of one TQ is defined by:
TQ =
BRP+1
ICLK
where ICLK is the frequency of the CAN module system clock and BRP is the
binary value of (BRP.7:0 + 1), calculated as follows:
BRP = 1 + BRP.0 + (2 x BRP.1) + (4 x BRP.2) + (8 x BRP.3) +
(16 x BRP.4) + (32 x BRP.5) + (64 x BRP.6) + (128 x BRP.7)
BRP is programmable from 1 to 256.
The value programmed into the CANBTC register has to be decremented by
1, because of the 8-bit size of the binary BRP value (BRP.7:0):
Bit-Timing Configuration Register (CANBTC) PRELIMINARY
BRPBTC = BRPCALC - 1
BRPCALC Result of bit-timing calculation.
1 BRPCALC 256
BRPBTC Value to be programmed into the CANBTC
register.
0 BRPBTC 255
Bit(s) Name Description
15:11 Reserved
10 SBG
1 The eCAN module will resynchronize on both rising and falling edges.
0 The eCAN module will resynchronise on the falling edge only.
9:8 SJW 1:0 Synchronization jump width. This determines the amount of time the synchronization
adapts. This value is enhanced by one when the CAN module accesses these
parameters.
7 SAM This parameter sets the number of samples used by the CAN module to determine
the actual level of the CAN bus. When the SAM bit is set, the level determined by
the CAN bus corresponds to the result from the majority decision of the last three
values. The sample points are at the sample point and twice before with a distance
of 1/2 TQ.
1 The CAN module will sample three times and make a majority decision.
The triple sample mode shall be selected only for bit rate prescale values
greater than 4 (BRPCALC > 4).
0 The CAN module samples only once at the sampling point.
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