Omron C200HW-PRM21 Operation Manuals page 37

Performance
Message cycle time
A message consists of an action frame (request or send/request frame) and a
reply frame (acknowledge or response frame). The message cycle time is
composed of the frame transmission times, the transmission delay times, the
station delay time and the bus idle time.
T = t
MC ACTION-FRAME
The station delay time is the time the slave needs for decoding the request
and generating an acknowledge or response frame.
The bus idle time is the time between an acknowledgement or response of
the slave and a new request from the master. Part of this time is used for
synchronisation (t = 33 t
SYN
PROFIBUS has different formats for the action frame and the reply frame.
The frames can have a fixed format (with no data field or with a data field of 8
octets) or a variable format (with a variable data field length).
A general formula for the message cycle time:
t = (9+n1) x 11 + (9+n2) x 11 + 2 x 0 + 30 + 37 t
MC
= (265 + 11n) t
where: n1 = number of action data bytes
n2 = number of reply data bytes
n = n1 + n2
The formula is based upon the following assumptions:
• The action frame and response frame have a variable format.
• The transmission delay times are negligible.
• t
= 30 t
STATION-DELAY BIT
• t
= 37 t
IDLE BIT
Live list check time
Each bus cycle the master requests the FDL (Fieldbus Data Link) status of
one of the stations connected to the network, except for the master stations
that have been entered in the LAS (List of Active Stations). The stations are
checked in sequence.
Each master is designated a certain range of slaves that it has to check. This
range is determined by the station addresses of the masters connected to the
network and the value for the parameter HSA (Highest Station Address).
A master checks the station addresses one higher than his own address up to
the next master address. If there is no master with a higher address, the
master checks until the value of HSA and starts again with checking from
station address 0.
If the station that is being checked is present and functions correctly, the
check time is approximately:
t = t
GAP_REQ REQ_FRAME
= 6 x 11 + 6 x 11 + 2 x 0 + 30 + 37 t
= 200 t
+ t + 2 x t
REPLY-FRAME TRANSMIT_DELAY
).
BIT
BIT
(typical value for the ASIC SPC3)
+ t + 2 x t
RES_FRAME TRANSMIT_DELAY
BIT
Section 3-2
+ t + t
STATION-DELAY IDLE
BIT
+ t + t
STATION-DELAY IDLE
BIT
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