3.3 Calculating PFH-d Value and Maximum Reaction Time

3.3.1 Calculating PFH-d value

Use 1 × 10⁻⁹ as the PFH-d value for SimpleCAN when calculating the total PFH-d.

3.3.2 Calculating maximum reaction time

The maximum reaction time of SimpleCAN is the user-configured timeout for the network. Since the timeout depends on the cycle time, both terms are described below.

3.3.2.1 Cycle time

The minimum cycle time depends on the baud rate and on how the nodes in the network are configured. Simplifier Manager checks this to make sure that the cycle time is valid for the configuration, and displays an error if it is too short.

Simple guideline: the cycle time should be at least the number of SimpleCAN IDs on the bus + 2 milliseconds. For example, 4 IDs → 6 ms. This is a requirement at a baud rate of 125 kbit/s, but it can be used for higher baud rates as well.

T_cycle = N_IDs + 2

3.3.2.2 Timeout

The recommended timeout is 2 × cycle time + 5 ms. For example: 20 ms cycle time → 45 ms timeout. This makes sure that two dropped or corrupted packets in a row do not result in a timeout. A shorter timeout of 1 × cycle time + 5 ms is possible, but it only allows one dropped packet without a timeout occurring.

Recommended timeout:

T_timeout = T_cycle × 2 + 5

Alternative, stricter timeout for a shorter reaction time:

T_timeout = T_cycle × 1 + 5

Number of transmitted IDs on the SimpleCAN bus	Cycle time (ms)	Timeout (ms), recommended	Timeout (ms), alternative
2	4	13	9
3	5	15	10
4	6	17	11
5	7	19	12
6	8	21	13
7	9	23	14
8	10	25	15
…	…	…	…
15	17	39	22
16	18	41	23
17	19	43	24
18	20	45	25
…	…	…	…
61	63	131	68
62	64	133	69
63	65	135	70
64	66	137	71

Table 3.1: Cycle time and timeout calculations.