28: AS-INTERFACE MASTER COMMUNICATION
« FC4A MICROSMART USER’S MANUAL » 28-5
Quantities of Slaves and I/O Points
The quantity of slaves that can be connected to one AS-Interface master module is as follows.
• Standard slaves: 31 maximum
• A/B slaves: 62 maximum
The limits for slave quantities given above apply when the slaves are either all standard slaves or are all A/B slaves.
When 62 A/B slaves (with four inputs and three outputs) are connected, a maximum of 434 I/O points (248 inputs and 186
outputs) can be controlled by one AS-Interface master module.
When using a mix of standard slaves and A/B slaves together, the standard slaves can only use addresses 1(A) through
31(A). Also, when a standard slave takes a certain address, the B address of the same number cannot be used for A/B
slaves.
AS-Interface Bus Topology and Maximum Length
The AS-Interface bus topology is flexible, and you can wire the bus freely according to your requirements.
When repeaters or extenders are not used, the bus length can be 100m (328 feet) at the maximum.
The FC4A-AS62M AS-Interface master module can use two repeaters to extend the bus length to 300m.
AS-Interface Bus Cycle Time
The AS-Interface bus cycle time is the amount of time required for a master to cycle through every slave on the bus.
The information for each slave is continuously transmitted over the bus in sequence, so the AS-Interface bus cycle time
depends on the quantity of active slaves.
• When up to 19 slaves are active, the bus cycle time is 3 ms.
• When 20 to 62 slaves are active, the bus cycle time is 0.156 × (1+N) ms where N is the number of slaves.
When A slave and B slave have the same address number (e.g. 12A and 12B), the two slaves are alternately updated each
cycle. Therefore, when the system consists of 31 A slaves and 31 B slaves, then the AS-Interface bus cycle time will be
10 ms.
Maximum AS-Interface Bus Cycle Time
• When 31 slaves are connected, the maximum bus cycle time is 5 ms.
• When 62 slaves are connected, the maximum bus cycle time is 10 ms.
High Reliability and Security
The AS-Interface employs a transfer process of high reliability and high security. The master monitors the AS-Interface
power supply voltage and data transmitted on the bus, and detects slave failures and data errors.
Even when a slave is replaced or a new slave is added during operation, the AS-Interface master module need not be shut
down and can continue uninterrupted communication with other active slaves on the bus.
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