Campbell Scientific CR5000 Measurement and Control Module - Manual (Page 157)

Section 7. Measurement Instructions
7-31
CANBUS (Dest, SDMAddress, TimeQuanta, TSEG1, TSEG2, ID, DataType,
StartBit, NumBits, NumVals, Multiplier, Offset)
The CANBUS instruction is used to measure and control the SDM-CAN
interface.
Multiple CANBUS instructions may be used within a program. The initial
function of the instruction is to configure the SDM-CAN interface when the
datalogger program is compiled. Subsequent instructions can be used to
determine what data is passed between the CAN-bus network and the
datalogger, set and/or read the SDM-CAN's internal switches, and read and/or
reset detected errors.
The SDMTrigger instructioncan be used to trigger simultaneous measurements
from one or more SDM-CANs and other SDM devices connected to the
datalogger. When the SDMTrigger instruction is encountered in a program, it
broadcasts a special SDM message which causes all the SDM-CAN devices to
copy the last data values captured from the CAN-bus into the working data
buffers. Refer to the SDM-CAN manual for additional help.
The CANBUS instruction has the following parameters:
Parameter
& Data Type Enter
Dest
The Dest parameter is a variable array in which to store the results of the
measurement. It must be an array of sufficient size to hold all of the values
that will be returned by the function chosen (defined by the DataType
parameter).
SDMAddress The SDMAddress parameter defines the address of the SDM-CAN with
which to communicate. Valid SDM addresses are 0 through 14. Address 15
is reserved for the SDMTrigger instruction.
The SDM address is entered as a base 10 number, unlike older, jumper-
settable SDM instruments that used base 4.
TimeQuanta
Three time segments are used to set the bit rate and other timing parameters
for the CAN-bus network, TimeQuanta, TSEG1, and TSEG2. These
parameters are entered as integer numbers. The relationship between the
three time segments is defined as:
t t t t
bit q TSEG TSEG
= + +
1 2
The first time segment, the synchronization segment (S-SG), is defined by
the TimeQuanta parameter. To calculate a suitable value for TiimeQuanta,
use the following equation:
TimeQuanta t
q
= * * 8 10 6
where tq = the TimeQuanta. There are between 8 and 25 time quanta in the
bit time. The bit time is defined as 1/baud rate.
TSEG1
The second time segment, TSEG1, is actually two time segments known as
the propagation segment and phase segment one. The value entered is
determined by the characteristics of the network and the other devices on the
network. It can be calculated as:
T t t
SEG TSEG q 1 1
= /