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chipFORTH networks 7,000 micros


Switchplan's problem was that in large modern office buildings floor layouts need to be rearranged without having to re-wire the lights.

What for one tenant may be 100 separate offices, some big some small, may for the next tenant be a single open plan office. In the first case, individual light switches will be needed. In the second, multiple switches at each entrance, all wired in parallel, will be needed. The solution chosen was to have many single chip micros each controlling a local region of switches and lights. Then to link the micros together for co-operative tasks and to use a PC for supervisory control and operator interface.

Schematic of chipFORTH based Lighting control system

Each local controller (LC) can react to two switches, infrared personnel detectors, dimmer controllers and can run two fluorescent lamps or sets of lamps. By setting variables held in an EEPROM, an LC can be made to react in different ways and to belong to a number of groups, potentially site wide.

An area controller (AC) concentrates communications between up to 100 LCs on each of four 9.6 Kbaud links and multiple ACs are then connected to a PC. The building manager can monitor access, control lighting groups, set groupings for night, day and holiday set-ups, examine light usage and, when necessary, reorganise the way the whole building's lights operate from the PC. The system is theoretically capable of handling 20,000 LCs and the largest configuration installed to date has 7,000 on line.

Both the LC, a masked single chip 8031, and the AC, an expanded 8032 with 32Kbyte ROM and 64Kbyte RAM, were programmed by COMSOL using chipFORTH. Phil Leach, Switchplan's chief systems engineer was particularly impressed by the way interactive development helped debug the area controllers.

"These are complex, time critical units running five serial links and three independent tasks. With the AC connected to both the PC and the LCs during development, we could control the tasks, examine the local database, drive I/O and really see what was going on".

Just in case you were thinking, "OK so Forth's good for small single chip programs but not for my big application," the PC runs a user-configurable full mimic-diagram package capable of showing many hundreds of room layouts. It can be configured for other link protocols, trends sensor changes, animates 100 sensor changes per second reported by the network. And it is written in FORTH. But that's another story see MIMIC.

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