hi-3111pstf Holt Integrated Circuits, Inc., hi-3111pstf Datasheet - Page 14

• Manufacturer Part Number: hi-3111pstf
• Description: Avionics Can Controller With Integrated Transceiver
• Manufacturer: Holt Integrated Circuits, Inc.

BIT TIMING
The CAN protocol supports a broad range of bit rates, from a
few kHz up to 1MHz (
3110 is limited to 40kHz by the permanent dominant timeout
protection of the transceiver). Every node on the network
has it’s own clock generator (typically a quartz oscillator),
however the bit rate must obviously be the same for every
node on the bus.
configurable to generate the nominal bit rate as a function of
it’s own oscillator frequency, f
a time quanta (TQ) clock, whose period t is related to the
oscillator frequency by a Baud Rate Prescaler value, BRP as
follows:
The TQ clock is used to construct the bit time in terms of time
quanta, such that one time quantum, Tq, equals one TQ
clock period, t , as shown in figure 8 below.
The CAN system nominal bit rate (BR) is defined in terms of
the nominal bit time, t , as
Therefore, the nominal bit rate is related to the TQ clock
period by the following relationship
BR = 1/(t x (number of time quanta per bit))
Clock
OSC
TQ
TQ
TQ
Sync
Seg
Tq
t
t
OSC
TQ
b
Therefore, each CAN node must be
Note:
t =
TQ
BR = 1/t
Prop Seg + Phase Seg 1
2•
the minimum bit rate of the HI-
OSC
BRP/f
Nominal bit time, t
. This is done by generating
TSeg1 =
b
OSC
TQ
HOLT INTEGRATED CIRCUITS
b
Sample
Figure 8. CAN Bit Time
Point
Phase Seg2
(2)
(1)
TSeg2 =
(3)
HI-3110
14
The CAN standard divides the bit time into four segments,
namely, synchronization segment (Sync Seg), propagation
time segment (Prop Seg), phase buffer segment 1 (Phase
Seg1) and phase buffer segment 2 (Phase Seg2). This is
illustrated in figure 8. The HI-3110 fixes the Sync Seg at
1Tq. Prop Seg and Phase Seg1 are treated as one time
segment, TSeg1, which is programmable from 2Tq to 16Tq.
Phase Seg2 is a second time segment, TSeg2, which is
programmable from 2Tq to 8Tq (
are valid, see below for examples).
Synchronization Segment (Sync Seg)
The Sync Seg is the first segment of the bit time and is used
to synchronize the various nodes on the bus. A bit edge is
expected to occur within the Sync Seg.
Propagation Time Segment (Prog Seg)
The Prog Seg is used to compensate for physical delays on
the bus, which include signal propagation delay time on the
bus and internal node delay times. For two nodes A and B
communicating on the bus, Prog Seg must be greater than
or equal to the sum of both nodes internal delays plus twice
the bus line propagation delay between the two nodes.
Baud Rate Prescaler
Sync
Seg
TSeg1
Note:
Not all combinations
TSeg2