Texas Instruments TMS320x281 series, Справочное руководство

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Bit-time = (TSEG1
reg
+ 1) + (TSEG2
reg
+ 1) + 1
Bit-time = TSEG1 + TSEG2 + 1
3.1.3 Bit Configuration Parameters for 150-MHz CAN Clock
CAN Module Initialization
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Where bit-time is the number of time quanta (TQ) per bit. SYSCLKOUT is the CAN module system clock
frequency, which is the same as the CPU clock frequency. BRP is the value of BRP
reg
+ 1
(CANBTC.23-16).
Bit-time is defined as follows:
In the above equation TESG1
reg
and TSEG2
reg
represent the actual values written in the corresponding
fields in the CANBTC register. The parameters TSEG1
reg
, TSEG2r
eg
, SJW
reg
, and BRP
reg
are
automatically enhanced by 1 when the CAN module accesses these parameters. TSEG1, TSEG2 and
SJW, represent the values as applicable per
Figure 3-2 .
This section and Section 3.1.4 provide example values for the CANBTC bit fields for various CAN module
clocks, bit rates and sampling points. Note that these values are for illustrative purposes only. In a
real-world application, the propagation delay introduced by various entities such as the network cable,
transceivers/ isolators must be taken into account before choosing the timing parameters.
Table 3-1 shows how the BRP
reg
field may be changed to achieve different bit rates with a BT of 15 for an
80% SP.
Table 3-1. BRP Field for Bit Rates (BT = 15, TSEG1
reg
= 10, TSEG2
reg
= 2, Sampling Point = 80%)
CAN Bus Speed BRP CAN Module Clock
1 Mbps BRP
reg
+1 = 10 15 MHz
500 kbps BRP
reg
+1 = 20 7.5 MHz
250 kbps BRP
reg
+1 = 40 3.75 MHz
125 kbps BRP
reg
+1 = 80 1.875 MHz
100 kbps BRP
reg
+1 = 100 1.5 MHz
50 kbps BRP
reg
+1 = 200 0.75 MHz
Table 3-2 shows how to achieve different sampling points with a BT of 15.
Table 3-2. Achieving Different Sampling Points With a BT of 15
TSEG1
reg
TSEG2
reg
SP
10 2 80%
9 3 73%
8 4 66%
7 5 60%
Table 3-3 shows how BRP
reg
field may be changed to achieve different bit rates with a BT of 10 for an
80% sampling point.
Table 3-3. BRP Field for Bit Rates (BT = 10, TSEG1
reg
= 6, TSEG2
reg
= 1, Sampling Point = 80%)
CAN Bus Speed BRP CAN Module Clock
1 Mbps BRP
reg
+1 = 15 10 MHz
500 kbps BRP
reg
+1 = 30 5 MHz
250 kbps BRP
reg
+1 = 60 2.5 MHz
125 kbps BRP
reg
+1 = 120 1.25 MHz
100 kbps BRP
reg
+1 = 150 1 MHz
50 kbps BRP
reg
+1 = 300 0.5 MHz
eCAN Configuration 70 SPRU074F – May 2002 – Revised January 2009
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