ScanTool STN1100 FRPM - Manual (Page 16)

STN1100
16 of 23 www.obdsol.com STN1100FRPMA
9.0 CAN Message Reception
For most users, CAN message reception works “out
of the box”, as configured by default. However, for
those users who wish to take full advantage of the
STN11xx’s CAN architecture, it is important to
understand what goes on behind the scenes.
You will notice that the flowchart in Figure 3 is
simply a more detailed version of the flowchart from
Figure 2. Therefore, in this section we will omit the left
half of the flowchart, and describe what happens when
the incoming CAN frame is identified as an ISO 15765
CAN frame.
If the RTR bit is set, the frame is determined to be a
remote frame. As long as it is not discarded by the
block filters, it gets sent over UART.
If the frame is not a remote frame, additional
processing takes place. The protocol control
information (PCI) byte is processed to determine
whether it is a valid ISO 15765-2 frame, and what type
Figure 3 – CAN Message Reception
CAN Frame from
Network
Flow Control Filters
added using STFAFC
Process PCI
Pass Filters
added using STFAP
Flow Control On?
set via ATCFC
ID Type
Look for Rx ID in
11-bit FC ID Pairs
added using STFAFCP
Transmit
Flow Control
Frame
Discard CAN
Frame
Block Filters
added using STFAB
Transmit
CAN Frame
on UART
CAN HW Filter
set via ATCF/ATCM
no match
match
match
ISO15765 Frame
Remote
Frame?
no
yes
Valid
ISO15765-2
First Frame?
yes
no
yes
no
11 bit
29 bit
no match
no match
no match
not found
match
match
found
ISO11898 Frame