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.TL
Data Frame Format for the CAN Gauge Interface
.AU
Sam Anthony
.AI
.LP
The Gauge Interface receives parameter values from other nodes in the vehicle via the CAN bus.
It also accepts frames from a host PC for calibration.
The format of these calibration, or
.I control ,
frames are the subject of this document.
.NH 1
Parameters
.LP
The Interface listens for 6 parameters on the bus:
.nr step -1 1
.IP \n+[step].
Tachometer
.IP \n+[step].
Speedometer
.IP \n+[step].
Analog 1
.IP \n+[step].
Analog 2
.IP \n+[step].
Analog 3
.IP \n+[step].
Analog 4
.LP
Each of these parameters has an associated CAN ID and a calibration table; thus, there are 6 IDs and 6 tables.
The Interface listens for these IDs and uses the tables to lookup output signal values to drive he gauges.
Each table has 32 rows, each of which contains a key and a value.
The keys and values are each 32-bit unsigned integers.
Numbers are transmitted in big-endian order in frames' DATA FIELD.
.NH 1
Frames
.LP
In addition to the parameter frames, there are two types of
.I control
frame:
.B "Table Control" ,
and
.B "ID Control" .
.NH 2
Table Control Frame
.LP
The Table Control Frame is used to read and write rows of the calibration tables.
It is an extended frame with DLC=8.
It may be either a DATA FRAME: to write to a table\(emor a REMOTE FRAME: to read from a table.
.PP
The Table Control Frame has extended ID
.B 12720XXh .
The LSB,
.I X ,
inticates which table, and which row of the table, to read or modify.
The upper 3 bits of
.I X
indicate one of the 6 tables [0, 5].
The lower 5 bits of
.I X
indicate one of the table's 32 rows [0, 31].
.begin dformat
style bitwid 0.15
Table Control ID
28-8 12720h
7-5 Table
4-0 Row
.end
.LP
The DATA FIELD contains a row of the table.
The row is composed of two 32-bit unsigned integers: a key and a value.
They are transmitted in big-endian order.
.begin dformat
style bitwid 0.07
style recspread 0
Table Control DATA FIELD
7-0 D0
7-0 D1
7-0 D2
7-0 D3
7-0 D4
7-0 D5
7-0 D6
7-0 D7
noname
31-0 Key
31-0 Val
.end
.LP
Upon receiving a Table Control DATA FRAME, the Interface will write the key and value to the row of the table specified in the ID.
.PP
In the case of a REMOTE FRAME, the Interface will read the row of the table specified in the ID, and respond with a DATA FRAME containing the key and value of the row.
.NH 2
ID Control Frame
.LP
The ID Control Frame is used to read or modify the CAN ID associated with one of the 6 parameters.
It is an extended frame with DLC=8.
It may be either a DATA FRAME: to modify\(emor a REMOTE FRAME to read.
.PP
The ID Control Frame has extended ID
.B 127210Xh .
The least significant nibble,
.I X ,
indicates one of the 6 parameters [0, 5].
.begin dformat
style bitwid 0.15
ID Control ID
28-4 127210h
3-0 X
.end
.LP
The DATA FIELD contains the CAN ID of the parameter specified in
.I X .
It may be either a standard or an extended ID.
In the case of a standard 11-bit ID, DLC=2 and the ID is sent as a 16-bit number.
In the case of an extended 29-bit ID, DLC=4 and the ID is sent as a 32-bit number.
The numbers are sent big-endian in both cases.
DLC can be used to determine whether the ID is standard or extended.
.begin dformat
style bitwid 0.08
style recspread 0
ID Control DATA FIELD (11-bit Std. ID)
7-0 D0
7-0 D1
noname
15-11
10-0 Std. ID
.end
.begin dformat
style bitwid 0.08
style recspread 0
ID Control DATA FIELD (29-bit Ext. ID)
7-0 D0
7-0 D1
7-0 D2
7-0 D3
noname
31-29
28-0 Ext. ID
.end
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