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External Interface Requirements

User Interfaces

The user interface to the system is designed to allow the user to set up the system, set schedules, and control individual or groups of devices. The system provides a graphical user interface to each of these. The user interface also provides the user with system status information. The user may query the system database for usage and weather history.

Hardware Interfaces

The Lazy Grounds KeeperÔ system makes use of one of the computer's serial ports to talk to the external Relay Control. This port needs to be dedicated to the system and not shared with other processes or devices. The system uses a standard RS-232 serial interface to communicate between the software and the physical devices. This port is connected to a Relay Control, which captures the signals and opens or closes the switches for the pumps, valves and sprinklers. The other external modules such as the weather monitoring unit and the moisture sensors are interfaced through this device.

The Relay Control will use the RS-232 protocol, and will transmit and receive at 9600 baud. The relay unit is a custom design that allows for the unique addressing of each physical device and the routing of command to that device. The relay unit shall be modular and expandable up to the limit of 65500 addressable devices.

The Relay Control has the ability to maintain the current state should the system need to be shutdown. If the system goes off line without telling the relay to hold state, the Relay Control will allow the devices to change to their "rest" state. The "rest" state for the system is the pumps off, the valves and sprinklers open. This is so the irrigation lines may be run by hand should the system be off line for an extended period of time. If the system has put the Relay in a hold state, has gone off line, and cannot be brought back on line, the Relay has a release button that puts the devices in a "rest" state.

Software Interfaces:

The system is designed to run as a program within the Windows 95 operating system. The software will be compliant with Windows 98 when it ships. The package is designed to work with the operating system and make use of the operating system to provide the underlying support and operating environment.

Lazy Grounds Keeper is not compatible with Windows NT. Windows NT will not allow the system to access and control the serial port in a manner necessary.

The Lazy Grounds Keeper is compatible with Windows 3.1 and Windows for Workgroups 3.11.

Lazy Grounds Keeper may also have compatibility issues with any other software packages that interface and use serial ports. The system takes over one of the ports and may have signals interrupted by programs or devices that scan those ports. Because the system will periodically request status from devices and modules, this port needs to always be available when the system is on.

Communication Interfaces:

Through the Relay Control the system is able to communicate with each of the devices in the irrigation system. Each physical device has a unique address in the system. The control software can send a signal to any one of the devices. This signal can tell a device to open, close, or request the current state of the device.

The system uses the RS-232 protocol and standard to talk to the devices. The system sends and receives data at a rate of 9600 baud. The system uses an eight bit data, one stop bit to talk to the Relay Control. Each command is composed of 5 - 8 bit words. The first two are combined to form the address of the receiving device. This will allow for more then 65000 devices in the system. The next 8 bits compose the message being sent to or from the device. The last 16 bits form the address of the device sending the message. Devices will accept commands to close, stop, open, start, return state or return current value. Pump commands are start, stop, or return current state. Valve and sprinkler commands are open, close, and return current state. Weather module and water flow/pressure sensors return value. The device will then answer with current state information. Only the control software may start communication. Other devices can then respond, once queried. The one exception is a device will send the control software a notice when a state has changed without a request to change .

One of the addressable devices is the Relay Control. The control software can tell the Relay to accept change of state commands or to hold state on the devices.

At 9600 baud it will take the system less then 6 seconds to send a change of state command to 600 devices, and receive responses. For a maximum system with 65500 devices it would take just over 10 minutes. These are maximum transfer rates. the system will not send a change of state to that many devices at that speed. Opening that many valves that fast would potentially cavitate the pump and crack water lines. Closing valves that fast could produce a water hammer that could brake valves. For that reason command are staggered to prevent damage to the system.

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