Enabling Communication Block; Selecting Scanning Speed - gefran 850 Installation And Instruction Manual

5.19.2.2. Enabling communication block

The communication block page is automatically enabled
when you select "Enabled" block type.
If you select "Disable", the parameter configuration will be
stored in memory by the software program, ready to be
reused at a later time with no need for a new configuration.

5.19.2.3. Selecting scanning speed

Communication blocks are executed by alternating two
tasks, referred to as SPEED=LOW and SPEED=HIGH. Each
communication block may be associated with one of the
two tasks to obtain the desired parameter scanning speed.
Master communication is managed every 20ms; effective
scanning times depend on this time, the slave device's
latency time and the communication speed set.
Example:
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with the following set-up:
MCB.01 SPEED=HIGH
MCB.02 SPEED=LOW
MCB.03 SPEED=LOW
MCB.04 SPEED=LOW
The communication sequence will be:
...MCB.01...MCB.02...MCB.01...MCB.03...MCB.01...
MCB.04...
In the case of ACCESS=WRITE ONLY objects, the same
value of a controller variable may be sent to multiple slave
noes with a node number between consecutive NODE and
NODE_MAX values.
In this case, scanning time is lengthened proportionately.
Example:
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⬅
with the following set-up:
MCB.01 SPEED=HIGH NODE=1 NODE_MAX=3
MCB.02 SPEED=LOW
MCB.03 SPEED=LOW
MCB.04 SPEED=LOW
The communication sequence will be:
...MCB.01 NODE=1...MCB.02...MCB.01 NODE=2...
MCB.03...MCB.01 NODE=3...MCB.04...
80209C_MHW_850-1650-1850_01-2020_ENG_pag. 242
Scanning time also depends on the baud rate used (MASTER_
KBAU=19200, 38400, 57600, 115200) and the latency time of
the slave's response.
Example:
850/1650/1850 connection with Gefran 19200 baud devices:
- Power controllers: GTF
- Controllers and programmers: 400/401, 450, 600/1200/1300,
800/1600/1800, 2500, 650/1250/1350, 850/1650/1850
- Indicators and alarm units: 4/40 T/B, 40TB, 2400, 650L/1250L
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With a latency time for Modbus communication in the slave of 0
to 20ms, the total duration of a message will be a maximum of:
(TX message=4.2ms) + (Response latency=20ms) +
(RX message=4.2ms) =
28.4ms (+ time of management of the RTS signal, if any)
Therefore:
• With 1 object: update every 40ms
• With 2 objects, one of which has SPEED=HIGH while the
other has SPEED=LOW: update 1 = update 2 = every 80ms
• With 3 objects, one of which has SPEED=HIGH while two
have SPEED=LOW: update 1 = 80ms, update 2 = update 3
= every 160ms
Example:
850/1650/1850 connection with Gefran 19200 baud devices:
- Power controllers: GFX4/GFXTERMO4/GFX4-IR/GFW
➡
⬅
With a latency time for Modbus communication in the slave of
0 to 5ms, the total duration of a message will be a maximum of:
(TX message=4.2ms) +
(RX message=4.2ms) =
13.4ms (+ time of management of the RTS signal, if any)
Therefore:
• With 1 object: update every 20ms
• With 2 objects, one of which has SPEED=HIGH while the
other has SPEED=LOW: update 1 = update 2 = every 40ms
• With 3 objects, one of which has SPEED=HIGH while two
have SPEED=LOW: update 1 = 40ms, update 2 = update 3
= every 80ms
Only if the instrument is connected will the effective update
time for each communication block in the variable UPD.x
with x from 1 to 20 be reported in the set-up page.
(Response latency=5ms) +