Questions and Answers
What is the minimum time period a node must wait before transmitting after the previous transmission has ended?
What is the maximum number of bytes that can be sent in a frame?
What type of connector is recommended for harsh environments?
What is the purpose of the first byte in a fragmented frame?
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What happens when a device needs to send more than 8 bytes of data?
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What is the role of the application layer?
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What is the significance of the first byte being '00' in a fragmented frame?
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Why is care required when handling hard-wired connections?
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What is the maximum allowed current for a power supply on a DeviceNet network using thick or flat wire?
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Which topology does DeviceNet utilize?
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What is the maximum size of the data field in a DeviceNet frame?
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What is the medium access control method used by DeviceNet?
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What is the power supply specification for DeviceNet cable power?
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What type of connector does the DeviceNet system utilize?
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What happens if a message larger than the data field size is sent in a DeviceNet frame?
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What is the termination requirement for DeviceNet's bus topology?
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What is the primary disadvantage of Xon-Xoff flow control?
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What is the purpose of 'zero insertion' in the Xon-Xoff flow control protocol?
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Which of the following is NOT a characteristic of the RS-232 interface standard?
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Which of the following is NOT a valid frame type used in the Fieldbus Control protocol?
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What is the role of the 'Control' field in a Fieldbus Control frame?
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Which of the following network topologies is NOT supported by the Fieldbus Control protocol?
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Which of the following protocols is standardized as IEC 61158?
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What is the primary purpose of the 'Frame Check Sequence' field in a Fieldbus Control frame?
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Study Notes
Physical Layer (Connectors)
- Transmission uses barrier strips or screw type terminations
- Hard-wired (unsealed) connection: ends of the cable are 'live' when removed from node and still connected to bus infrastructure, requiring insulation of exposed ends
- Mini (sealed) connector: 18 mm round connector recommended for harsh environments (field connections)
Data-Link Layer (Fragmentation)
- Any device needing more than 8 bytes of data sent will cause fragmentation
- A frame can only contain 8 bytes of data; first byte used for reassembly
- Fragmentation: 7 bytes of data sent at a time, with first byte facilitating reassembly
- First byte significance:
- 00: First fragment (number 0)
- 41-7F: Intermediate fragment (lower 6 bits of byte is fragment number)
- 80-FF: Last fragment (lower 6 bits of byte is fragment number)
Data-Link Layer (Frame Format)
- DeviceNet frame: small data field (8 bytes), messages larger than this need to be fragmented
- Frame fields: flag, address, control, information, frame check sequence
Physical Layer (Network Power)
- One or more 24 V power supplies can be used to power devices on DeviceNet network
- Power supplies should be dedicated to DeviceNet cable power only
- 8 A current limit on thick/flat wire and 3 A limit on thin wire must not be exceeded
Data-Link Layer (Medium Access)
- Medium access control method: carrier sense multiple access with non-destructive bit-wise arbitration (CSMA/NBA)
- Node wishing to transmit must defer to any existing transmission
Application Layer
- Provides user with standard set of messaging services for all three networks
- Allows user to connect to any network and configure/collect data from any network
- Saves time and effort during system configuration, no routing tables or added logic required
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Description
Quiz on data link layer concepts, including transmission, connectors, and cable connections.