PXS20RM Datasheet, PDF (616/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

FlexCAN Module
24.3.4.2 Control Register (CTRL)
This register is defined for specific FlexCAN control features related to the CAN bus, such as bit-rate,
programmable sampling point within an Rx bit, Loop Back Mode, Listen Only Mode, Bus Off recovery
behavior and interrupt enabling (Bus-Off, Error, Warning). It also determines the Division Factor for the
clock prescaler. This register can be accessed at any time, however some fields must be changed only
during either Disable Mode or Freeze Mode. Find more information in the fields descriptions ahead.
Base + 0x0004
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
R
W
PRESDIV
RJW
PSEG1
PSEG2
RE-
SET:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
16 17 18 19 20 21 22
R
W
BOFF ERR_ CLK_
_MSK MSK SRC
LPB
TWR RWR
N_MS N_MS
K
K
0
RE-
SET:
0
0
0
0
0
0
0
23 24 25 26 27 28 29 30 31
0
SMP
BOFF
_REC
TSYN LBUF
LOM
PROPSEG
000000000
= Unimplemented or Reserved
Figure 24-6. Control Register (CTRL)
PRESDIV — Prescaler Division Factor
This 8-bit field defines the ratio between the CPI clock frequency and the Serial Clock (Sclock)
frequency. The Sclock period defines the time quantum of the CAN protocol. For the reset value, the
Sclock frequency is equal to the CPI clock frequency. The Maximum value of this register is 0xFF,
that gives a minimum Sclock frequency equal to the CPI clock frequency divided by 256. For more
information refer to Section 24.4.8.4, Protocol Timing. This bit must be written in Freeze mode only.
Sclock frequency = CPI clock frequency / (PRESDIV + 1)
RJW — Resync Jump Width
This 2-bit field defines the maximum number of time quanta¹ that a bit time can be changed by one
re-synchronization. The valid programmable values are 0–3. This bit must be written in Freeze mode
only.
Resync Jump Width = RJW + 1.
PSEG1 — Phase Segment 1
This 3-bit field defines the length of Phase Buffer Segment 1 in the bit time. The valid programmable
values are 0–7. This bit must be written in Freeze mode only.
Phase Buffer Segment 1 = (PSEG1 + 1) x Time-Quanta.
1. One time quantum is equal to the Sclock period.
24-16
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor