DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

or not depends on the number of receiving CAN nodes. The command sent depends on the
data written to the FILHIT bits of the RXB1CTRL register of the MCP2515. The
meaning of these filter bits is described in Section 5.3.20.4 and a program execution flowchart is
shown in Figure 5.37. Figure 6.5 shows the contents of this MCP2515 register.
Figure 6.5 RXB1CTRL – Receive Buffer 1 Control Register Bit Definitions [44].
The $random() function is used to determine which command is going to be sent to the
CAN nodes. Details of the $random() function are covered in Section 5.2.8.3. To generate a
random value to represent the command to send to the CAN node(s), the following block of
code was executed:
integer seed_value, random_value;
random_value = $random(seed_value) % 7;
random_value = abs(random_value);
This block of code returns a value between 0 and 6 which corresponds to the list of commands
summarized in Table 6.3. This random value is then sent out to one or both CAN nodes as a
command setting the appropriate bits in the FILHITx registers on the node(s). The receiving
CAN node(s) then perform the required command and send the resulting data back to the 1 –
Wire® Master which then stores the data contiguously in the DS1996 1 – Wire® slave devices.
The results of this test are presented in Table 6.4.
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