Omron CQM1-ARM21, Руководство по эксплуатации

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Introduction
Section 1-1
6
Master
Slave
receives
Slave Response
Send Pause
sends
Master Request
receives
Master Request
sends
Slave Response
Master Pause
sends
Master Request
receives
Master Request
Transaction
time
(1 -2 bit times) Slave Pause
(2,5 to 5,5 bit times)
Security A request or response will be judged invalid if it contains one of the following
types of error:
Start bit error The initial pulse is not negative.
Alternating error Two consecutive pulses do not have different polarity.
No information Pulses are not detected in periods of
( * )
.
.
n s 6
0 5
1 0
−
+
µ
.
Parity error The sum of all information bits is not even.
End bit error The last pulse is not positive.
Length error Pulses are detected during the master or slave pause.
Upon an invalid or missing slave response, a master station will retry to
access the slave. If this fails, the slave will be taken out of the list of active
slaves. The master will cyclically try to re-initialise the slave in the inclusion
phase.
Performance
The cycle time of an AS-Interface network depends on the number of slaves
that the master has to exchange I/O data with. The AS-Interface specification
defines the maximum bus cycle time as follows:
if n = 33
n * Master request = n * (14 Bit) = n * 84
µ
s = 2722
µ
s
+ n * Master pause = n * (3 Bit) = n * 18
µ
s (synchr. slave) = 594
µ
s
+ n * Slave response = n * (7 Bit) = n * 42
µ
s = 1386
µ
s
+ n * Send pause = n * (2 Bit) = n * 12
µ
s (min.) = 396
µ
s
= Tcycle = n * (26 Bit) = n * 156
µ
s (min.) = 5148
µ
s
where n is the number of all AS-Interface requests during data exchange in
the AS-Interface cycle and in the inclusion phase, including one repetition. In
normal operation, n will be the number of slaves plus 2.
With less than 31 slaves, the AS-Interface cycle time will be shorter. In
principle, each slave less will decrease the cycle time by 156
µ
s, but the
master is allowed to lengthen the send pause up to 500
µ
s, as long as the
total cycle time does not exceed the stated maximum.
To calculate the CQM1-ARM21’s cycle time, see 3-3, Performance.