User`s guide

190
CHAPTER 8 - CFW-08 OPTIONS AND ACCESSORIES
Figure 8.35
- Times required during the communication of a message
T
11 bits
= Time to transmit one word of the message.
T
entre bytes
= Time between bytes (can notbe longer than T
3,5x
).
T
3,5x
= Minimum interval to indicate the begin and the
end of the message (3,5 x T
11bits
).
Signal
Time
T
11 bits
T
3,5 x
T
between bytes
T
3,5 x
Message
Communication
T
11 bits
T
3,5x
9600 bits/s
1.146 ms
4.010 ms
19200 bits/s
573

s
2.005 ms
38400 bits/s
285

s
1.003 ms
4.
Repeat steps 2 and 3 until the eight displacements have
been realized.
5.
Repeat the steps 1 to 4, by using the next byte message
until the whole message have been processed.
The end content of the CRC variable is the value of the CRC
field that is transmitted at the end of the message. The least
significant part is transmitted first (CRC), only then the most
significant part (CRC+) is transmitted.
Times between messages:
In the RTU mode there is no specific character that indicates
thebeginningortheendof amessage.Thusthe onlyindication
for the beginning or the end of a new message is the data
transmission absence in the network by a minimum time of
3.5 times the time required for transmission of one data word
(11 bits). Thus if a message is initiated after elapsing of the
minimum time required without transmission, the network
elements assume that the received character represents the
beginning of a new message. In similar mode, after this time
has elapsed, the network elements will assume that the
message has been ended.
If during the transmission of a message, the time between
the bytes is longer than this minimum required time, the
message will be considered invalid, since the inverter will
discard the already received bytes and will mount a new
message with the bytes that are being transmitted.
The table below shows the time for three different
communication rates.
Table 8.10
- Times required during the communication of a message