Omron C200HW-PRM21 Operation Manuals page 38

Performance
22
If the station is not present, the master stops waiting for an answer after the
slot-time (one of the bus parameters). The check time in this case is:
t = t
GAP_REQ REQ_FRAME
= 6 x 11 + 100 + 37 t
= 203 t
The formulas are based upon the following assumptions:
• The transmission delay times are negligible.
• t
= 30 t
STATION-DELAY BIT
• t
= 37 t
IDLE BIT
• t
= 100 t
SLOT BIT
Token cycle time
The token cycle time is the time each master station requires to process and
transfer the token. It is composed of the token frame time, the transmission
delay time and the bus idle time.
t = t
TC TOKEN-FRAME
The bus idle time contains the station delay time of the receiver and the
synchronisation time.
A general formula for the token cycle time:
t = 3 x 11 + 0 + 37 t
TC
= 70 t
The formula is based upon the following assumptions:
• The transmission delay time is negligible.
• t
= 37 t
IDLE BIT
Examples
The two figures below give an indication of the fieldbus cycle time. In each
figure the bus cycle time is calculated for four different baud rates (500 kbit/s,
1500 kbit/s, 3000 kbit/s, and 12000 kbit/s).
The first figure shows the effect of the number of slaves on the bus cycle time.
The values of the parameters are:
n
ns
nr
Baud rate
The fieldbus cycle time is calculated with the formula for a single master
system.
The bus cycle time increases when the number of slaves increases due to the
fact that the total number of data bytes that needs to be transferred increases.
+ t + t
SLOT IDLE
BIT
BIT
(typical value for the ASIC SPC3)
(configurable)
+ t + t
TRANSMIT_DELAY IDLE
BIT
BIT
= 4 (number of data bytes per slave)
= variable on the x-axis
= 0
= variable per curve
Section 3-2