AS-i is a system in which exchange management is ensured by a single master which, by scanning the bus, calls each slave in succession and awaits a response.
Communication series frame for slaves with standard AS-i address settings:
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4 data bits (D0 to D3), which are the image of inputs or outputs according to the type of interface,
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4 parameter bits (P0 to P3), which are used to set the operating modes of the interface.
Communication series frame for slaves with extended address settings:
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3 or 4 data bits, which are the image of inputs (4 bits, D0 to D3) or outputs (3 bits, D0 to D2) depending on the type of interface,
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3 parameter bits (P0 to P2), which are used to set the operating modes of the interface.
All slave devices connected to the AS-i bus are identified by at least one "I/O Code" and one "ID code" which completes the functional identification of the slave.
Some slaves have an ID1 code, which defines the internal functions of the slave: on Analog slaves, for example, ID1 shows the slave's analog channel number.
NOTE: The frame base is the same for Analog slaves as it is for Discrete slaves.
There is ascending compatibility between AS-i and AS-i V2. This means that all slaves on the market are supported by SAY 1000.
Each slave connected to the AS-i bus must have an address which lies between 1 and 31, either with "Bank" /A, or with "Bank" /B for extended address settings.
The slaves delivered from the factory have the address 0 (the address of the slave is memorized in a non-volatile format).
Addresses are programmed using a specialized addressing terminal.
NOTE: When replacing a faulty slave whose address has been set, the address of the slave to be replaced can be updated automatically.
All standard address setting slaves connected to the AS-i bus are identified by:
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An I/O Code (input/output distribution code),
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An identification code, which completes the functional identification of the slave.
All extended address setting slaves connected to the AS-i bus are identified by:
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An I/O Code (input/output distribution code),
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An identification code which completes the functional identification of the slave.
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An ID1 code which defines the internal functions of the slave,
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An identification code (ID2) which completes the functional identification of the slave.
These identifications allow the AS-i master to recognize the configuration, which is present on the bus.
These different profiles have been developed by the AS-i Association. They are used to distinguish between input, output and mixed modules, "intelligent" device families, etc.
Maximum Number of Inputs/Outputs
On the same bus, an AS-i bus can support a maximum of:
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31 4I and/or 4O standard address setting slaves, with addresses from 1 to 31
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62 extended address setting slaves with 4I and/or 3O , using addresses from 1 A/B to 31 A/B.
This makes it possible to manage a maximum of 248 inputs +186 outputs (thus 434 inputs/outputs) when all extended slaves have 4 inputs and 3 outputs.
The AS-i cable is a twin-wire link on which communications and power supply for the connected devises are transmitted.
The link does not need to be twisted.
The cross-section of wires can be from 2 x 0.75 mm2, 2 x 1.5 mm2 or 2 x 2.5 mm2, according to the current consumed by the devices.
Topology and Maximum Length of AS-i Bus
The topology of the AS-i bus is with flexible and adapted to meet the users needs (point to point, on line, tree structure etc.).
In every case, the total length of all the branches of the bus must not exceed 100 meters without a relay.
This is the cycle time between slave(s) and the TSX SAY 1000 module.
The AS-i system always transmits information, which is the same length to each slave on the bus. The AS-i cycle time depends upon the number of slaves connected to the bus in the presence of functioning slaves.
The scan time t represents the exchange time between a master and n active slaves (a maximum of 31 on /A or /B).
So, for:
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up to 19 active slaves, t = 3ms
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20 to 31 active slaves t = (1+n) * 0.156ms
When two slaves A and B have the same address, each slave in the pair is scanned every two cycles.
This means that for 31 extended address setting slaves configured in /A, + 31 extended address setting slaves configured in /B. the scan time will be 10 ms.
Maximum cycle time:
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maximum 5 ms for 31 standard or extended address setting slaves,
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maximum 10 ms for 62 extended address setting slaves.
Reliable operation is ensured by the transmission process used (Manchester current and coding modulation). The master monitors the line supply voltage and the data sent. It detects transmission errors as well as slave failures, and sends the information to the PLC.
Exchanging or connecting a new slave during operation does not disturb communications between the master and the other slaves.
