Systec Electronic CANopen ChipF40, Системное руководство

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CANopen ChipF40 Operation
L-1062e_9 © SYS TEC electronic GmbH 2010
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8.8 Analog Input Operation
8.8.1 Handling Analog Values
This section provides general information on data storage of analog
values in a CANopen frame.
The CANopen Standard CiA 401 defines that all analog values till 15
bit have to be stored as 16-bit value aligned left with a sign bit. On the
CANopen ChipF40 all A/D-conversion values are stored with 10-bit
data. Consequently, for each analog channel, two data bytes must be
transmitted.
These data bytes are stored and transmitted on the CAN bus as shown
in
Table 25 .
Byte 2 Byte 1
Sign 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
+/- Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 0 0 0 0 0
Table 25: Storage of Analog Values
On the CAN bus, first byte 1 and then byte 2, is transmitted.
8.8.2 Formula for Calculating the Analog Input Value
The formula listed below is used to calculate a voltage value of an
analog input from the A/D-conversion result:
ADC resolution
V hex
V
range voltage conversion D A result
AIn
2
/
/ /
/
•
=
The following example will explain the use of this formula in more
detail:
over CAN transmitted A/D-value
= 012A0H (4768 dec)
voltage range = 5V (standard supply on pins
VAREF and VAGND)
logical resolution ADC = 15 Bit
analog input value (AI) = 0,727V