Measurement Computing DBK70 - Manual (Page 51)

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For example, it is acceptable to have one channel enabled with an update rate of 100mS or 2 channels
enabled with an update rate of 200mS each. But, it is not recommended to have an update rate for 2
enabled channels at 100mS each.
These limitations are due to the fact that the networks on some vehicles can easily be overwhelmed by
request messages that are broadcast too frequently. When the network traffic is too great, the vehicle
network may malfunction temporarily. If the specified rates grossly exceed the recommended rates, the
DBK70 will attempt to adjust the rates.
There is no soft or hard limit on CAN bus. Most fast CAN PGNs do not need to be requested. They
automatically update by their source module without a request message. When issuing request messages
on the CAN network, limit the aggregate request rate to about 100 per second.
The values for Message Send Rate range from 0 to 32000 milliseconds.
Msg 1 and Msg 2
The “Sending a Request Message” Panel
Located in the “Detailed View” tab of the Data Base Item View
The Msg 1 and Msg 2 fields specify a message that is to be broadcast by the DBK70 on the vehicle’s
network at the rate specified by the Message Send Rate parameter.
The codes to be used for the message fields (Msg 1 and Msg 2) are hexadecimal byte values, i.e., 00 to FF.
The maximum length is dependent on the type of vehicle data bus to be used, e.g., 12 bytes for J1850.
Request messages are used to obtain data when the data to be processed by an output channel is not
normally available on the vehicle’s data bus but can be obtained by sending a request for it.
Typically only one message needs to be sent as a request message to an electronic control module.
In the Detailed View PidPRO will gray-out and deny access to the Msg1 and Msg2
data fields when a Message Rate of zero is entered. If no message is desired [for a
particular database record] perform these to steps in the order shown:
(1) Delete the Msg1 and Msg2 data fields.
(2) Assign zero for the value of the Message Send Rate.