Acromag AcroPack AP560, User Manual

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AcroPack Series AP560 CAN Bus Interface Module
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BIT Timing Register 1
BTR1 configures the CAN protocol bit timing segments in terms of time
quanta (Tq) and sets the number of sampling points. This register can be read
anytime and written only in init mode (MODE<2:0> bits set to <1xx> in the
CTRL0 register).
Table 20 BTR1 (Write 0x1A, Read 0xD8)
BIT FUNCTION
3:0 TSEG1 3:0 – Time Segment 1 bits <3:0>
Tseg1 = Prop Seg + Phase Seg1 of the CAN protocol bit
timing specification. Bits TSEG1-3:0 specify the number of
time quanta in Prop Seg + Phase Seg1. Note: Not all
combinations are valid, since Prop Seg + Phase Seg1 ≥
Phase Seg 2. The CAN protocol states that the minimum
number of Tq in a bit time shall be 8.
0000 – Not valid
0001 – Tseg1 = 2 Tq clock cycles
0010 – Tseg1 = 3 Tq clock cycles
0011 – Tseg1 = 4 Tq clock cycles
⁞
1111 – Tseg1 = 16 Tq clock cycles
Notes: ARINC825 states that the sample point shall not be
less than 75% of the bit time. In this case, Tseg1 should be
a minimum of 5Tq for Phase Seg2(Tseg2) = 2 Tq and
SJW = 1 Tq.
6:4 TSEG2 2:0 – Time Segment 2 bits <2:0>
Tseg2 = Phase Seg2 of the CAN protocol bit timing
specification. Bits TSEG2-2:0 specify the number of time
quanta in Phase Seg2. Not all combinations are valid, since
Phase Seg 2 must be greater than SJW.
000 – Not valid
001 – Tseg2 = 2 Tq clock cycles
010 – Tseg2 = 3 Tq clock cycles
011 – Tseg2 = 4 Tq clock cycles
⁞
111 – Tseg2 = 8 Tq clock cycles
7 SAMP – Samples per bit
This bit configures how many samples are taken per bit
0 – one sample per bit
1 – three samples per bit
Notes: ARINC825 states that there shall be only one
sample per bit. Furthermore, it is recommended to sample
only once at higher CAN bit rates. Bit sampling occurs at
the end of the Phase Seg 1.