JVL MIS17 Series, User Manual

Page: 264 / 367

264 JVL Industri Elektronik A/S - User Manual - Integrated Stepper Motors MIS17x, 23x, 34x, 43x
9.9 More about program timing
The firmware is structured so that one program instruction is executed for each pass of
the main loop, which takes approximately 30 microseconds ( μ s) without CANopen,
without serial communications and when the motor is not running. The Main Loop Time
is termed MLT in the following text.
A single program line in MacTalk can generate more than one instruction. For example,
assigning a constant value to a register uses two instructions: First load the value to the
internal stack and then Store from the stack to the target register. The above table in Mo-
tor Connections , page 346 reflects this operation.
The main loop time will vary depending on a number of factors: The serial communica-
tions speed and load, whether CANopen is installed, and the CANopen communications
speed and load.
Serial communications on the RS-485 line can load the motor up to 1% at 19.200 baud,
which is insignificant, but at the maximum baud rate of 921.600 the communications can
load the motor up to 45%, which would result in an MLT of ~60 μ s.
When CANopen firmware is installed, the basic MLT will change from 30 to 90 μ s with
no communications.
When loading the CANbus with communications, the MLT can rise significantly. For ex-
ample, when using seven transmit PDOs with an event timer value of 1 ms and a CANbus
link speed of 500 kbits/s, the MLT can rise to 150-200 μ s. Also using RS-485 communi-
cations at high baud rates can result in even longer MLT values. However, this scenario
is very unlikely.
Note: In applications where program timing is critical, tests must be performed
to ensure that timing is satisfactory when communication is running according
to conditions used in production!