PIC32MX OBD Evaluation Board

PIC32MX OBD Evaluation Board

Requirements

Basics of communication protocol

PIC module communicates with control unit via Bluetooth. In most cases communication is initiated by control unit via sending 'query' message to PIC module. Messages are composed from ASCII characters only which simplifies debugging (one can send message using any popular terminal emulator). Following is an example of query which reads value from channel 8 of A/D converter:

---------------------------------------
| SOF | ID | CMD | DATA | CHSUM | EOF |
---------------------------------------
|  <  | A  |  A  |  08  |  EA58 |  >  |
---------------------------------------

where

SOF	start of frame
ID	module ID (e.g. analog module)
CMD	command
DATA	data payload (up to 1kB of bytes, 2kB of ASCII characters )
CHSUM	CRC-CCITT checksum (optional)
EOF	end of frame

Packets can be amended with checksum to verify their integrity. The checksum is calculated as 16bit CRC-CCITT of ASCII codes of all ASCII characters in packet excluding SOF and EOF. This feature is turned off by default and has to be explicitly enabled - see below.

Response from PIC module can have following formats depending on the result of operation and if there is any data payload to be returned.

command succeeded, no data payload

--------------------------------
| SOF | ID | ACK | CHSUM | EOF |
--------------------------------
|  <  | A  |  A  |  A122 |  >  |
--------------------------------

command failed

--------------------------------------
| SOF | ID | NAK | ERR | CHSUM | EOF |
--------------------------------------
|  <  | A  |  N  |  01 |  F054 |  >  |
--------------------------------------

command succeeded, there are data to be returned immediately in one packet

---------------------------------------
| SOF | ID | PKT | DATA | CHSUM | EOF |
---------------------------------------
|  <  | A  | 00  | 1234 |  6B45 |  >  |
---------------------------------------

command succeeded, data are to be returned later in several packets

--------------------------------         ---------------------------------------  ---------------------------------------
| SOF | ID | ACK | CHSUM | EOF |         | SOF | ID | PKT | DATA | CHSUM | EOF |  | SOF | ID | PKT | DATA | CHSUM | EOF |
--------------------------------   ...   ---------------------------------------  ---------------------------------------
|  <  | A  |  D  |  8523 |  >  |         |  <  | A  | 01  | 1234 |  6C21 |  >  |  |  <  | A  | 00  | 1234 |  6BFC |  >  |
--------------------------------         ---------------------------------------  ---------------------------------------

where

SOF	start of frame
ID	module ID (e.g. A/D module)
PKT	packet number (00 for last packet)
ACK	acknowledge (A for no data payload, D for data to be sent in following packet(s))
NAK	negative acknowledge
ERR	error code
DATA	data payload (up to 1kB of bytes, 2kB of ASCII characters )
CHSUM	CRC-CCITT checksum
EOF	end of frame

Summary of currently supported module IDs:

A	PIC A/D converter
C	Controller Area Network (CAN) module
E	communication with car ECUs
L	Carmon logger
M	reserved
P	core PIC module
R	RFID module
Q	data acquisition module

Generic NAK responses (shared by all modules)

N01	unknown module ID or command
N02	invalid value
N03	underlying module busy
N04	I/O error
N05	CRC error

Following chapters provide more details about communication with particular modules.

PIC core module

PIC core module provides API for

configuring parameters of communication with master module
getting EEPROM parameters
setting EEPROM parameters
getting date and time
setting date and time
reading temperature sensor
low level communication with devices on I²C bus

Commands

c	calculate CRC checksum for given data
C	configure communication parameters
d	get date and time
D	set date and time
t	get temperature from MCP9801 temperature sensor
e	get EEPROM parameter
E	set EEPROM parameter
i	read data from I²C device
I	write data to I²C device

Calculating CRC checksum

Query
----------------------------------------------
| SOF | P | c | TYPE | P1..P4 | D1..DN | EOF |
----------------------------------------------

where

TYPE	1b	s - 16-bit CRC-CCITT calculated by software (only P4 used); d - CRC calculated by DMA module
P1	1b	0 - input data not reflected (MSB first); ≠0 - input data reflected (LSB first)
P2	1b	length of CRC polynom (1..32)
P3	4b	CRC polynom
P4	4b	CRC seed
D1..DN	Nb	data in form of ASCII HEX

Response
-------------------------------------------
| SOF | P | 00 | CRC | TIME | CHSUM | EOF |
-------------------------------------------

where

CRC	4b	calculated CRC
TIME	2b	time in μs the calculation process took

Error codes

N02	Invalid parameters provided

Configuring communication parameters

-------------------------------------
| SOF | P | C | CRCEN | CHSUM | EOF |
-------------------------------------

where

CRCEN	1 byte	!= 0 - packets amended with CRC-CCITT checksum

Error codes

EINVAL	Invalid parameters provided

Setting EEPROM parameter

-------------------------------------------
| SOF | P | E | NUM | VALUE | CHSUM | EOF |
-------------------------------------------

where

NUM	1b	parameter number
VALUE	Nb	parameter value

Error codes

EINVAL	Invalid parameter number

Valid parameters

num	size	description
01	2b	PID autoscan mode - PID sample rate in [ms]
02	Nb	PID autoscan mode - PID groups

Getting EEPROM parameter

Query
-----------------------------------
| SOF | P | e | NUM | CHSUM | EOF |
-----------------------------------

where

NUM	1b	parameter number

Response
--------------------------------------
| SOF | P | 00 | VALUE | CHSUM | EOF |
--------------------------------------

where

VALUE	Nb	parameter value

Error codes

EINVAL	Invalid parameter number

Setting date and time

-------------------------------------------------------------
| SOF | P | D | YYYY | MM | DD | hh | mm | ss | CHSUM | EOF |
-------------------------------------------------------------

where

YYYY	4 chars	year
MM	2 chars	month (01 to 12 where January = 01)
DD	2 chars	day of month (01 to 31)
hh	2 chars	hours since midnight (00 to 23)
mm	2 chars	minutes after the hour (00 to 59)
ss	2 chars	seconds after the minute (00 to 61), allows for up to two leap seconds

Error codes

EINVAL	Failed to set the date or time - provided date or time invalid

Getting date and time

Query
-----------------------------
| SOF | P | d | CHSUM | EOF |
-----------------------------

Response
--------------------------------------------------------------------
| SOF | P | 00 | YYYY | MM | DD | hh | mm | ss | mmm | CHSUM | EOF |
--------------------------------------------------------------------

where

YYYY	4 chars	year
MM	2 chars	month (01 to 12 where January = 01)
DD	2 chars	day of month (01 to 31)
hh	2 chars	hours since midnight (00 to 23)
mm	2 chars	minutes after the hour (00 to 59)
ss	2 chars	seconds after the minute (00 to 59)
mmm	3 chars	milliseconds (000 to 999)

Error codes

??	??

Getting temperature from MCP9801 temperature sensor

Query
-----------------------------
| SOF | P | t | CHSUM | EOF |
-----------------------------

Response
-------------------------------------
| SOF | P | 00 | TTTT | CHSUM | EOF |
-------------------------------------

where

TTTT	2b	temperature coded as two's complement (see packet format below)

Format of TTTT packet:

bit#	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
	Sign	2⁶ °C	2⁵ °C	2⁴ °C	2³ °C	2² °C	2¹ °C	2⁰ °C	2^-1 °C	2^-2 °C	2^-3 °C	2^-4 °C	0	0	0	0

Error codes

??	??

Reading from I²C device

Query
--------------------------------------------
| SOF | P | i | A1 | A2 | LN | CHSUM | EOF |
--------------------------------------------

Response
----------------------------------------------
| SOF | P | 00 | D1 | ... | DN | CHSUM | EOF |
----------------------------------------------

where

A1	1b	I²C device address
A2	1b	register address
LN	1b	number of bytes to be read (0..255)
D1..DN	Nb	data

Error codes

??	??

Writing to I²C device

Query
-------------------------------------------------------
| SOF | P | I | A1 | A2 | D1 | ... | DN | CHSUM | EOF |
-------------------------------------------------------

where

A1	1b	I²C device address
A2	1b	register address
D1..DN	Nb	data to be written

Error codes

??	??

Carmon logger

Carmon logger module provides API for

configuring operating mode of Carmon logger device
determining last sector written by Carmon logger
reading sectors from the log device

Commands

C	configure the module
l	get number of last sector written by Carmon logger
R	read blocks from the log device according to provided parameters
r	read subsequent blocks from the log device according to parameters previously set via 'R' command

Configure the module

Query
------------------------------------
| SOF | L | C | MODE | CHSUM | EOF |
------------------------------------

where

MODE	1b	operating mode (0..configuration, 1..autonomous, 2..assisted)

ACK response
-----------------------------
| SOF | L | A | CHSUM | EOF |
-----------------------------

Read sectors from the log device according to provided parameters

Query
--------------------------------------------------------
| SOF | L | R | CONF | SECSTART | BLKNUM | CHSUM | EOF |
--------------------------------------------------------

where

CONF	1b	configures how sectors are transfered to the master
SECSTART	4b	number of 1st sector to be read
BLKNUM	4b	number of blocks to be read

Format of CONF word:

bit#	7	6	5	4	3	2..0
	NA	NA	NA	1/0..binary/ASCII mode	1/0..block is/is not compressed	number of sectors in block (1-8)

ACK response - standard ASCII mode
-----------------------------------------------
| SOF | L | A | SN | B1D1..B1DN | CHSUM | EOF |
-----------------------------------------------
-----------------------------------------------
| SOF | L | A | SN | B2D1..B2DN | CHSUM | EOF |
-----------------------------------------------
...
-----------------------------------------------
| SOF | L | A | SN | BMD1..BMDN | CHSUM | EOF |
-----------------------------------------------
ACK response - binary mode
---------------------------------------------------
| DLE | STX | SN | B1D1..B1DN | CHSUM | DLE | ETX |
---------------------------------------------------
---------------------------------------------------
| DLE | STX | SN | B2D1..B2DN | CHSUM | DLE | ETX |
---------------------------------------------------
...
---------------------------------------------------
| DLE | STX | SN | BMD1..BMDN | CHSUM | DLE | ETX |
---------------------------------------------------

where

SN	1b	sequence number (01-FF); incremented with each packet; useful for detection of packet loss
BxD1..BxDN	Nb	Xth data block (CONF[2..0] sectors)

note: When operating in binary mode, each DLE data byte is replaced with sequence of two DLE bytes.

RFID module

RFID module provides API for

obtaining records from RFID reader via Bluetooth interface
manipulating records captured from RFID reader to the local permanent storage (SD card)

Commands

E	enable sending RFID records via Bluetooth
D	disable sending RFID records via Bluetooth
R	read logged records
C	remove logged records (clean up log file - its size is truncated to zero)

Enable sending RFID records via Bluetooth

Query
-----------------------------
| SOF | R | E | CHSUM | EOF |
-----------------------------

ACK response
-----------------------------
| SOF | R | A | CHSUM | EOF |
-----------------------------

Packets containing records from RFID reader
--------------------------------------------------------------------------------
| SOF | R | SN | YYYY | MM | DD | hh | mm | ss | mmm | RFID DATA | CHSUM | EOF |
--------------------------------------------------------------------------------

where

SN	sequence number (01-FF); incremented with each packet; useful for detection of packet loss
YYYY - mmm	timestamp of RFID record (with 1 millisecond resolution)
RFID DATA	RFID record (12 ASCII HEX characters)

Disable sending RFID records via Bluetooth

Query
-----------------------------
| SOF | R | D | CHSUM | EOF |
-----------------------------

ACK response
-----------------------------
| SOF | R | A | CHSUM | EOF |
-----------------------------

Read logged records one-by-one

Logged records are read from log device one by one. The reading process is initiated by “Read the first record” query. Response to that query contains the first logged record. Subsequent records are then returned as responses to “Read next record” queries. Response with no data payload indicates that all records have been read. The whole reading process can be restarted by sending “Read the first record” query again.

"Read the first record" query
--------------------------------
| SOF | R | R | F |CHSUM | EOF |
--------------------------------

"Read next record" query
--------------------------------
| SOF | R | R | N |CHSUM | EOF |
--------------------------------

Response containing logged record
--------------------------------------------------------
| SOF | R | 00 | TIMESTAMP1 | RFID DATA1 | CHSUM | EOF |
--------------------------------------------------------

where

TIMESTAMPx	timestamp of RFID record (YYYY - mmm)
RFID DATAx	RFID record (12 ASCII HEX characters)

Response with no data payload
------------------------------
| SOF | R | 00 | CHSUM | EOF |
------------------------------

Valid NAK responses

RN03	module currently busy either reading or writing (due to just received tag ID) a record

Read all logged records at once

In this case, log device sends all logged records at once. The process is initiated by “Read all records” query. The log device then sends all logged records, followed by one empty record indicating that all records have been sent. Each log record contains 8bit sequence number - the first record has sequence number set to '01', then it is incremented for each subsequent record. Once the sequence number reaches 'FF', it rolls over to '01'. '00' identifies the last record.

"Read all records" query
--------------------------------
| SOF | R | R | A |CHSUM | EOF |
--------------------------------

Response containing logged records
--------------------------------------------------------
| SOF | R | 01 | TIMESTAMP1 | RFID DATA1 | CHSUM | EOF |
--------------------------------------------------------
--------------------------------------------------------
| SOF | R | 02 | TIMESTAMP2 | RFID DATA2 | CHSUM | EOF |
--------------------------------------------------------
...
------------------------------
| SOF | R | 00 | CHSUM | EOF |
------------------------------

where

TIMESTAMPx	timestamp of RFID record (YYYY - mmm)
RFID DATAx	RFID record (12 ASCII HEX characters)

Valid NAK responses

RN03	module currently busy either reading or writing (due to just received tag ID) a record

Delete logged records

Query
-----------------------------
| SOF | R | C | CHSUM | EOF |
-----------------------------

ACK response
-----------------------------
| SOF | R | A | CHSUM | EOF |
-----------------------------

Valid NAK responses

RN10	module currently busy either reading or writing log record(s)
RN13	log device not available (e.g. SD card not present)

Analog data acquisition module

Analog data acquisition module provides mechanism for acquiring data from internal PIC A/D converter with following parameters.

10-bit resolution
up to 16 analog inputs
automatic channel scan mode
selectable conversion trigger source
16-word conversion result buffer
selectable buffer fill modes
eight conversion result format options

The acquisition module supports

single or continuous acquisition
auto, normal trigger modes
configurable trigger level and type (rising edge, falling edge)
up to 1024 samples per one conversion cycle
200us-1s sample rate

Function

When acquisition is started, the module goes through the following steps.

acquires pre-trigger number of samples
continues with data acquisition waiting for trigger condition to occur
detects the trigger condition
acquires post-trigger number of samples

Commands

C	set parameters of acquisition (trigger mode, sample rate, …)
R	run acquisition
S	stop acquisition

Configuration of acquisition mode

------------------------------------------------------------------------------
| SOF | Q | C | CH | AM |TM | TE | TP | SR | RR | PREN | POSTN | CHSUM | EOF |
------------------------------------------------------------------------------

where

CH	1b	channel
AM	1b	acquisition mode (1 - single, 2 - continuous)
TM	1b	trigger mode (1 - normal, 2 - auto (do not wait for trigger))
TE	1b	trigger event (1 - rising edge, 2 - falling edge)
TP	2b	trigger parameters, depends on TE
SR	2b	sample rate in form of 0xvvvu (where u: 0-us, 1-ms, 2-s)
RR	2b	refresh rate in form of 0xvvvu (where u: 0-us, 1-ms, 2-s)
PREN	2b	number of pre-trigger samples (0x0000..0x0400)
POSTN	2b	number of post-trigger samples (0x0000..0x0400)

Error codes

EINVAL	Configuration invalid (e.g. some of provided parameters is out of range

If running in 'auto' trigger mode, all acquired data are returned. In 'normal' trigger mode, summary of pre-trigger and post-trigger number of samples is returned. However, if number of pre-trigger samples is set to zero, then all acquired data are returned.

Run acquisition

-----------------------------
| SOF | Q | R | CHSUM | EOF |
-----------------------------

Error codes

01	??
02	??

Stop acquisition

-----------------------------
| SOF | Q | S | CHSUM | EOF |
-----------------------------

Error codes

01	??
02	??

Post processing module

Post processing module operates on data acquired by data acquisition module.

Configuration of post processing

---------------------------------------
| SOF | Q | P | M | PAR | CHSUM | EOF |
---------------------------------------

where

M	1b	ID of post processing module to be activated
PAR	xb	parameters specific to selected post processing module

Error codes

EINVAL	Configuration invalid (e.g. unknown ID of post processing module

Turn off post processing

----------------------------------
| SOF | Q | P | 00 | CHSUM | EOF |
----------------------------------

Signal identification post processing module

Collects various characteristics of acquired signal

Activate
--------------------------------------
| SOF | Q | P | 02 | A | CHSUM | EOF |
--------------------------------------

Format of data response
--------------------------------------------------------------------------------
| SOF | Q | 00 | MEAN | RMS | MIN | MAX | F1 | F2 | F3 | F4 | F5 | CHSUM | EOF |
--------------------------------------------------------------------------------

where

MEAN	2b	mean value
RMS	2b	square of RMS value of AC part of signal
MIN	2b	minimum of AC part of signal
MAX	2b	maximum of AC part of signal
F1 - F5	20b	frequencies of spectrum of acquired signal in form of <F(2b)MAG(2b)>

FFT post processing module

Performs FFT on test signal or signal acquired from A/D converter.

Activate
----------------------------------------------
| SOF | Q | P | 01 | A | LOG2N | CHSUM | EOF |
----------------------------------------------

where

LOG2N	1b	logarithm base 2 of the number of samples: N = 2^LOG2N

Test FFT post processing
---------------------------------------------
| SOF | Q | P | 01 | T | DATA | CHSUM | EOF |
---------------------------------------------

where

DATA	Nb	data used to calculate FFT

Controller Area Network (CAN) module

Commands/responses

A	analyze the bus
C	configure the module
s	obtain status of the module
S	send packet
R	packet received

Analyzing bus traffic

When attaching a node to the CAN bus we don't know much about, it is better to analyze the existing bus parameters as well as traffic before the node is allowed to actively participate in communication. Or, we may just want to take a look at what's happening on some CAN bus. As an example, modern cars use CAN bus to interconnect different electronic units and we may want to poke around - just out of curiosity. This is what analyzer mode is supposed to serve for. Following is generic packet format when working with analyzer.

-------------------------------------------
| SOF | C | A | MODE | DATA | CHSUM | EOF |
-------------------------------------------

where

MODE	1b	mode of analysis
DATA	xx	data specific to particular mode

Currently supported modes:

00	finish current analysis, generate report
01	generic snoop mode
02	address analysis
03	data analysis
04	timing analysis

Deactivating analyzer

Analyzer is deactivated by following packet:

----------------------------------
| SOF | C | A | 00 | CHSUM | EOF |
----------------------------------

Mode 01 - generic snoop mode

In this mode, all received CAN frames are immediately passed to master. It is possible to configure which part of frames are to be sent to master. That is useful in scenarios when we are interested just in particular information (e.g. IDs or data payload). This mode honors previously configured acceptance filter, so it is possible to focus on CAN frames with particular ID. Complete format of CAN frame sent to master:

--------------------------------------------------------------------
| SOF | C | R | 00 | TSTAMP | TYPE | ID | DLC | DATA | CHSUM | EOF |
--------------------------------------------------------------------

where

TSTAMP	2b	timestamp
TYPE	1b	message type (bit 0 - RTR (1 for remote frame), bit 1 - EID (1 for extended ID)
ID	4b	29-bit extended (TYPE[1] == 1) or 11-bit standard (TYPE[1] == 0) identifier
DLC	1b	data length code - 0..8
DATA	0..8b	data

Mode is activated in following way:

-----------------------------------------
| SOF | C | A | 01 | MASK | CHSUM | EOF |
-----------------------------------------

where

MASK	1b	Bitmask selecting which information is sent to master. Active if set to 1.
		bit 0 - TSTAMP
		bit 1 - TYPE
		bit 2 - ID
		bit 3 - DLC
		bit 4 - DATA

Error codes

?	?

Mode 02 - address analysis

This mode is used to obtain information about IDs appearing on the bus. Once activated, it starts listening to CAN bus and sends all new IDs found to the master. This mode honors previously configured acceptance filter, so it is possible to focus on CAN frames with just particular set of IDs. Up to 100 addresses are scanned. Format of CAN frame sent to master:

---------------------------------------
| SOF | C | R | 00 | ID | CHSUM | EOF |
---------------------------------------

where

ID	4b	29-bit extended or 11-bit standard identifier; all ones if ID buffer is full

Mode is activated in following way:

----------------------------------
| SOF | C | A | 02 | CHSUM | EOF |
----------------------------------

Error codes

?	?

Mode 03 - data analysis

The next step of this drill-down type of analysis is trying to determine what kind of information particular data carry. To help with that, data analysis mode provides for possibility to focus on particular frame and analyzing changes in its data payload. The goal is to associate those changes with changes in real world (e.g. change in speedometer value). Frame is sent to master only if change in specified portion of data payload is detected. Format of CAN frame sent to master:

----------------------------------------------
| SOF | C | R | 00 | ID | DATA | CHSUM | EOF |
----------------------------------------------

where

ID	4b	29-bit extended or 11-bit standard identifier
DATA	0..8b	data payload

Mode is activated in following way:

-----------------------------------------
| SOF | C | A | 03 | MASK | CHSUM | EOF |
-----------------------------------------

where

MASK	8b	Bitmask selecting which bits of data payload are undergoing process of comparison. One means particular bit participates in the process.

Error codes

?	?

Mode 04 - timing analysis

Timing analysis provides information about timing situation on the bus. In particular, it calculates total number of frames received during analysis as well as minimum and maximum time between two subsequent frames. That mode can be either used to obtain overall picture about load on the bus or (with combination of the filtering) it is possible to collect information about frames with just particular ID - e.g. frame rate as well as jitter can be determined. To commence the analysis, following frame is to be sent to master:

----------------------------------
| SOF | C | A | 04 | CHSUM | EOF |
----------------------------------

Once the analysis is finished by deactivation packet (see above), results are sent to master in following form:

----------------------------------------------------------
| SOF | C | 00 | FNUM | TTIME | TMIN | TMAX |CHSUM | EOF |
----------------------------------------------------------

where

FNUM	4b	number of frames received
TTIME	2b	total time of analysis - resolution 1ms
TMIN	2b	minimum time between packets - resolution 100us
TMAX	2b	maximum time between packets - resolution 100us

Error codes

?	?

Module configuration

----------------------------------------------
| SOF | C | C | NUM | CFG DATA | CHSUM | EOF |
----------------------------------------------

where

NUM	1b	Configuration number
CFG DATA	xx	configuration data specific to particular configuration number

Error codes

?	?

Configuration #1

Configures communication mode and speed.

-------------------------------------------------
| SOF | C | C | 01 | MODE | SPEED | CHSUM | EOF |
-------------------------------------------------

where

MODE	1b	0 - normal, 1 - disabled, 2 - loopback, 3 - listen only, 4 - listen all messages
SPEED	1b	0 - 1Mbit, 1 - 500kbit, 2 - 250kbit, 3 - 125kbit

Error codes

?	?

Configuration #2

Configures acceptance filter and mask. The CAN network is a broadcast type of network. A message transmitted by one node is received by all nodes in the network. Individual CAN nodes require a filtering mechanism to receive messages of interest. This filtering mechanism is provided by the CAN message acceptance filter and mask. Filtering is performed on the ID field of the CAN message.

---------------------------------------------------------
| SOF | C | C | 02 | MODE | FILTER | MASK | CHSUM | EOF |
---------------------------------------------------------

where

MODE	1b	bit 0 - if set, message type (specified via bit 1) is also compared; if cleared, bit 1 is ignored and both SID and EID messages can be received
		bit 1 - if cleared, SID messages are received; if set, EID messages are received
FILTER	4b	SID (EID) to be accepted
MASK	4b	specifies which ID bits should be compared (0 - particular bit is not compared)

Error codes

?	?

Obtaining module status

Query
-----------------------------
| SOF | C | s | CHSUM | EOF |
-----------------------------

Response
--------------------------------------------------------------------
| SOF | C | 00 | ERRSTS | TERRCNT | RERRCNT | RXDROP | CHSUM | EOF |
--------------------------------------------------------------------

where

ERRSTS	1b	Error state
		RXOVF (bit 6) - Receive buffer overflowed
		TXBO (bit 5) - Transmitter in Error State Bus OFF (TERRCNT ≥ 256)
		TXBP (bit 4) - Transmitter in Error State Bus Passive (TERRCNT ≥ 128)
		RXBP (bit 3) - Receiver in Error State Bus Passive (RERRCNT ≥ 128)
		TXWARN (bit 2) - Transmitter in Error State Warning (128 > TERRCNT ≥ 96)
		RXWARN (bit 1) - Receiver in Error State Warning (128 > RERRCNT ≥ 96)
		EWARN (bit 0) - Transmitter or Receiver is in Error State Warning
TERRCNT	1b	Transmit error counter
RERRCNT	1b	Receive error counter
RXDROP	1b	Number of packets dropped (not sent to master) due to high load on CAN bus

Sending a packet

Query
------------------------------------------------------
| SOF | C | S | TYPE | ID | DLC | DATA | CHSUM | EOF |
------------------------------------------------------

Ack response
-----------------------------
| SOF | C | A | CHSUM | EOF |
-----------------------------

where

TYPE	1b	message type (bit 0 - RTR (1 for remote frame), bit 1 - EID (1 for extended ID)
ID	4b	29-bit extended (TYPE[1] == 1) or 11-bit standard (TYPE[1] == 0) identifier
DLC	1b	data length code - 0..8
DATA	0..8b	data

Error codes

?	?

Module for communication with ECUs

Commands

C	set communication parameters
O	communication with OBD module

Communication with OBD module

-------------------------------------------
| SOF | E | O | MODE | PARS | CHSUM | EOF |
-------------------------------------------

where

MODE	1b	OBD mode
PARS	Nb	parameters - mode specific

Error codes

?	?

Configure OBD module

Query
-----------------------------------------
| SOF | E | O | C | PROTO | CHSUM | EOF |
-----------------------------------------

where

PROTO	1b	communication protocol
		0 - auto
		1 - KWP2000 normal
		2 - KWP2000 debug
		3 - KWP2000 combined with CAN (CAN must be configured via CAN specific commands)
		4 - CAN SID (11-bit identifier) 250 kbit
		5 - CAN SID 500 kbit
		6 - CAN EID (29-bit identifier) 250 kbit
		7 - CAN EID 500 kbit

Response
---------------------------------
| SOF | E | C | A | CHSUM | EOF |
---------------------------------

Show current data (read value of OBD PID)

Query
----------------------------------------------
| SOF | E | O | P | MODE | PID | CHSUM | EOF |
----------------------------------------------

where

MODE	1b	OBD mode - 0x01 for standard OBD PIDs, 0x21 for Toyota specific PIDs, …
PID	1b	OBD PID

Response
-----------------------------------------------
| SOF | E | P | 00 | PID | DATA | CHSUM | EOF |
-----------------------------------------------

where

PID	1b	OBD PID
DATA	Nb	OBD PID value

Show current data periodically for given list of PIDs

Query
--------------------------------------------------------------------------------
| SOF | E | O | p | SR | NF | NM | NS | LIST F | LIST M | LIST S | CHSUM | EOF |
--------------------------------------------------------------------------------

where

SR	2b	sample rate in [ms]
NF	1b	number of PIDs in 'fast' group
NM	1b	number of PIDs in 'medium' group
NS	1b	number of PIDs in 'slow' group
LIST F,M,S	Nb	list of PIDs for particular group

Response
-----------------------------------------------
| SOF | E | p | SN | PID | DATA | CHSUM | EOF |
-----------------------------------------------

where

SN	1b	sequence number (01-FF); incremented with each packet; useful for detection of packet loss
PID	1b	PID number
DATA	Nb	PID value

Stop showing current data periodically for previously given list of PIDs

Query
---------------------------------
| SOF | E | O | p | CHSUM | EOF |
---------------------------------

Response
-----------------------------
| SOF | E | A | CHSUM | EOF |
-----------------------------

Show Freeze Frame data

Query
---------------------------------------------
| SOF | E | O | F | FFN | PID | CHSUM | EOF |
---------------------------------------------

where

FFN	1b	Freeze Frame number
PID	1b	PID number

Response
-----------------------------------------------------
| SOF | E | F | 00 | FFN | PID | DATA | CHSUM | EOF |
-----------------------------------------------------

where

FFN	1b	Freeze Frame number
PID	1b	PID number
DATA	Nb	PID value

Read "confirmed" Diagnostic Trouble Codes (DTCs)

Obtaining the complete list of stored confirmed DTCs is two-step process. In the first step total number of stored DTCs is determined by reading current value of PID 01 - zero indicates that no DTCs were stored. After that list of DTCs is obtained by reading DTCs one by one starting from zero.

Query
----------------------------------------
| SOF | E | O | D | DTCN | CHSUM | EOF |
----------------------------------------

where

DTCN	1b	DTC number

Response
----------------------------------------
| SOF | E | D | 00 | DTC | CHSUM | EOF |
----------------------------------------

where

DTC	2b	DTC

Error codes

EINVAL	DTC with specified number does not exist

Clear/reset emission-related diagnostic information

Clears MIL, number of stored DTCs, confirmed as well as pending DTCs, freeze frame data, etc.

Query
---------------------------------
| SOF | E | O | R | CHSUM | EOF |
---------------------------------

Error codes

EIO	ECU cannot perform this operation under current conditions (e.g. engine running)

Problems found

there are no blocking capacitors nearby PIC - add some
missing pull-ups on μSD card signals

Resources

Source code can be browsed here using OpenGrok, “a wicked fast source browser”.

Table of Contents

PIC32MX OBD Evaluation Board

Requirements

Basics of communication protocol

Generic NAK responses (shared by all modules)

PIC core module

Commands

Calculating CRC checksum

Configuring communication parameters

Setting EEPROM parameter

Getting EEPROM parameter

Setting date and time

Getting date and time

Getting temperature from MCP9801 temperature sensor

Reading from I²C device

Writing to I²C device

Carmon logger

Commands

Configure the module

Read sectors from the log device according to provided parameters

RFID module

Commands

Enable sending RFID records via Bluetooth

Disable sending RFID records via Bluetooth

Read logged records one-by-one

Read all logged records at once

Delete logged records

Analog data acquisition module

Function

Commands

Configuration of acquisition mode

Run acquisition

Stop acquisition

Post processing module

Configuration of post processing

Turn off post processing

Signal identification post processing module

FFT post processing module

Controller Area Network (CAN) module

Commands/responses

Analyzing bus traffic

Deactivating analyzer

Mode 01 - generic snoop mode

Mode 02 - address analysis

Mode 03 - data analysis

Mode 04 - timing analysis

Module configuration

Configuration #1

Configuration #2

Obtaining module status

Sending a packet

Module for communication with ECUs

Commands

Communication with OBD module

Configure OBD module

Show current data (read value of OBD PID)

Show current data periodically for given list of PIDs

Stop showing current data periodically for previously given list of PIDs

Show Freeze Frame data

Read "confirmed" Diagnostic Trouble Codes (DTCs)

Clear/reset emission-related diagnostic information

Problems found

Resources

Schema