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Council Regulation (EEC) No 3821/85 of 20 December 1985 on recording equipment in road transport
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Some services are necessary to establish and maintain communication. They do not appear on the application layer. The services available are detailed in the following table:
Communication services
Service name | Description |
---|---|
StartCommunication | The client requests to start a communication session with a server(s) |
StopCommunication | The client requests to stop the current communication session |
TesterPresent | The client indicates to the server that it is still present |
[CPR_005] The StartCommunication Service is used for starting a communication. In order to perform any service, communication must be initialised and the communication parameters need to be appropriate for the desired mode.
[CPR_006] Upon receiving a StartCommunication indication primitive, the VU shall check if the requested communication link can be initialised under the present conditions. Valid conditions for the initialisation of a communication link are described in document ISO 14230-2.
[CPR_007] Then the VU shall perform all actions necessary to initialise the communication link and send a StartCommunication response primitive with the positive response parameters selected.
[CPR_008] If a VU that is already initialised (and has entered any diagnostic session) receives a new StartCommunication request (e.g. due to error recovery in the tester) the request shall be accepted and the VU shall be re-initialised.
[CPR_009] If the communication link cannot be initialised for any reason, the VU shall continue operating as it was immediately prior to the attempt to initialise the communication link.
[CPR_010] The StartCommunication Request message must be physically addressed.
[CPR_011] Initialising the VU for services is performed through a ‘ fast initialisation ’ method,
there is a bus-idle time prior to any activity,
the tester then sends an initialisation pattern,
all information which is necessary to establish communication is contained in the response of the VU.
[CPR_012] After completion of the initialisation,
all communication parameters are set to values defined in Table 4 according to the key bytes,
the VU is waiting for the first request of the tester,
the VU is in the default diagnostic mode, i.e. StandardDiagnosticSession,
the calibration I/O signal line is in the default state, i.e. disabled state.
[CPR_014] The data rate on the K-line shall be 10 400 Baud.
[CPR_016] The fast initialisation is started by the tester transmitting a wake-up pattern (Wup) on the K-line. The pattern begins after the idle time on K-line with a low time of Tinil. The tester transmits the first bit of the StartCommunication Service after a time of Twup following the first falling edge.
[CPR_017] The timing values for the fast initialisation and communications in general are detailed in the tables below. There are different possibilities for the idle time:
first transmission after power on, T idle = 300 ms.
after completion of a StopCommunication Service, T idle = P3 min.
[X1After stopping communication by time-out P3 max, T idle = 0.]
Editorial Information
Timing values for fast initialisation
Parameter | minimum value | maximum value | |
---|---|---|---|
Tinil | 25 ± 1 ms | 24 ms | 26 ms |
Twup | 50 ± 1 ms | 49 ms | 51 ms |
Communication timing values
Timing parameter | Parameter description | Lower limit values (ms) | Upper limit values (ms) |
---|---|---|---|
minimum | maximum | ||
P1 | Inter byte time for VU response | 0 | 20 |
P2 | Time between tester request and VU response or two VU responses | 25 | 250 |
P3 | Time between end of VU responses and start of new tester request | 55 | 5 000 |
P4 | Inter byte time for tester request | 5 | 20 |
[CPR_018] The message format for fast initialisation is detailed in the following tables:
StartCommunication request message
Byte # | Parameter Name | Hex value | Mnemonic |
---|---|---|---|
#1 | Format byte — physical addressing | 81 | FMT |
#2 | Target address byte | EE | TGT |
#3 | Source address byte | tt | SRC |
#4 | StartCommunication Request Service | 81 | SCR |
#5 | Checksum | 00-FF | CS |
StartCommunication positive response message
Byte # | Parameter Name | Hex value | Mnemonic |
---|---|---|---|
#1 | Format byte — physical addressing | 80 | FMT |
#2 | Target address byte | tt | TGT |
#3 | Source address byte | EE | SRC |
#4 | Additional length byte | 03 | LEN |
#5 | StartCommunication Positive Response Service Id | C1 | SCRPR |
#6 | Key byte 1 | EA | KB1 |
#7 | Key byte 2 | 8F | KB2 |
#8 | Checksum | 00-FF | CS |
[CPR_019] There is no negative response to the StartCommunication Request message, if there is no positive response message to be transmitted then the VU is not initialised, nothing is transmitted and it remains in its normal operation.
The purpose of this communication layer service is to terminate a communication session.
[CPR_020] Upon receiving a StopCommunication indication primitive, the VU shall check if the current conditions allow to terminate this communication. In this case the VU shall perform all actions necessary to terminate this communication.
[CPR_021] If it is possible to terminate the communication, the VU shall issue a StopCommunication response primitive with the Positive Response parameters selected, before the communication is terminated.
[CPR_022] If the communication cannot be terminated by any reason, the VU shall issue a StopCommunication response primitive with the Negative Response parameter selected.
[CPR_023] If time -out of P3max is detected by the VU, the communication shall be terminated without any response primitive being issued.
[CPR_024] The message formats for the StopCommunication primitives are detailed in the following tables:
StopCommunication request message
Byte # | Parameter Name | Hex value | Mnemonic |
---|---|---|---|
#1 | Format byte — physical addressing | 80 | FMT |
#2 | Target address byte | EE | TGT |
#3 | Source address byte | tt | SRC |
#4 | Additional length byte | 01 | LEN |
#5 | StopCommunication Request Service Id | 82 | SPR |
#6 | Checksum | 00-FF | CS |
StopCommunication positive response message
Byte # | Parameter Name | Hex value | Mnemonic |
---|---|---|---|
#1 | Format byte — physical addressing | 80 | FMT |
#2 | Target address byte | tt | TGT |
#3 | Source address byte | EE | SRC |
#4 | Additional length byte | 01 | LEN |
#5 | StopCommunication Positive Response Service | C2 | SPRPR |
#6 | Checksum | 00-FF | CS |
StopCommunication negative response message
Byte # | Parameter Name | Hex value | Mnemonic |
---|---|---|---|
#1 | Format byte — physical addressing | 80 | FMT |
#2 | Target address byte | tt | TGT |
#3 | Source address byte | EE | SRC |
#4 | Additional length byte | 03 | LEN |
#5 | negative Response Service Id | 7F | NR |
#6 | StopCommunication Request Service Identification | 82 | SPR |
#7 | responseCode = generalReject | 10 | RC_GR |
#8 | Checksum | 00-FF | CS |
This service does not require any parameter definition.
The TesterPresent service is used by the tester to indicate to the server that it is still present, in order to prevent the server from automatically returning to normal operation and possibly stopping the communication. This service, sent periodically, keeps the diagnostic session/communication active by resetting the P3 timer each time a request for this service is received.
[CPR_079] The message formats for the TesterPresent primitives are detailed in the following tables.
TesterPresent request message
Byte # | Parameter Name | Hex value | Mnemonic |
---|---|---|---|
#1 | Format byte — physical addressing | 80 | FMT |
#2 | Target address byte | EE | TGT |
#3 | Source address byte | tt | SRC |
#4 | Additional length byte | 02 | LEN |
#5 | TesterPresent Request Service Id | 3E | TP |
#6 | Sub Function = responseRequired = [yes no] | 01 02 | RESPREQ_Y RESPREQ_NO |
#7 | Checksum | 00-FF | CS |
[CPR_080] If the responseRequired parameter is set to ‘ yes ’ , then the server shall respond with the following positive response message. If set to ‘ no ’ , then no response is sent by the server.
TesterPresent positive response message
Byte # | Parameter Name | Hex value | Mnemonic |
---|---|---|---|
#1 | Format byte — physical addressing | 80 | FMT |
#2 | Target address byte | tt | TGT |
#3 | Source address byte | EE | SRC |
#4 | Additional length byte | 01 | LEN |
#5 | TesterPresent Positive Response Service Id | 7E | TPPR |
#6 | Checksum | 00-FF | CS |
[CPR_081] The service shall support the following negative responses codes:
TesterPresent negative response message
Byte # | Parameter Name | Hex value | Mnemonic |
---|---|---|---|
#1 | Format byte — physical addressing | 80 | FMT |
#2 | Target address byte | tt | TGT |
#3 | Source address byte | EE | SRC |
#4 | Additional length byte | 03 | LEN |
#5 | negative Response Service Id | 7F | NR |
#6 | TesterPresent Request Service Identification | 3E | TP |
#7 | responseCode = [SubFunctionNotSupported-InvalidFormat incorrectMessageLength] | 12 13 | RC_SFNS_IF RC_IML |
#8 | Checksum | 00-FF | CS] ] |
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