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As i understand the adress range on each line is 0-255 and 0 is reserved for linecoupler. Why have so many addresses if you only can connect 64? will it be possible in the future to add more devices. |
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The limit of 64 devices on a line is not only related to power consumption. It is also a bus load limit. Each device plugged on the bus make the impedance lower, which may interfere with the telegrams transmission. The goal of the repeaters is not only to separate the segments lines in terms of power supply, but also to regenerate the signals of the telegrams. You should also consider that repeaters do not use filtering table. So every telegram is propagated to all segments of the line, even if it is useless. It is not realy important for a small installation, but the right way is to extend over 64 devices by creating more lines using line couplers, and to extend lines with repeaters only when you reach 15 lines in your area and you don't want to add another area (which should not occur in a home). |
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First of all as somebody said, on one line you can connect more than 64 devices but you should use line coupler as repeater (disable filter table) and two power supplies (this way you make new segment). It will be one line and with address bigger than 64 and two segments. Moreover there are two popular types of power supply - 640mA and 320mA. It is said, that casual KNX device has a 5mA power consumption. 64 devices * 5mA = 320mA. But there are some devices that has bigger power consumption - LCD display, room operator etc, they are powered from bus. You can find power consumption value in tech. specyfication or sometimes in ETS at device properities->catalog entry. For example - Basalte push button (5 functions) with temperature sensor, without display and with LED backlight - consumpt 10mA - info from ETS. That's why for bigger instaltion than 30 devices you should use 640mA PS to be safe. PS I've heard about instalation, where more than 80 devices are connected to bus to PS 640mA. It works. But I think some more devices or some traffic on bus can stop whole instalation. Why? If voltage on bus goes under 19V (I'm not sure with this value..) than devices will not work - less than 19V is signal for reset devices. For the records, the value Tommy is speaking about is 18V. Actually this value is not a trigger for reset. BCUs recognize a voltage drop below 18V as a HW interrupt. The corresponding procedure to be executed is the "Save" routine. This will save in EEPROM current values found in RAM, for example to restore group object status before failure. This depends on ETS configuration also. When the voltage come back again, the opposite routine is called "UsrInit", which, correspondingly, loads the application program and retrieves status values from EEPROM to RAM, as needed.
(Aug 15 '10 at 10:02)
Massimo
The normal operation range for KNX on TP1 is beetween 21 and 29V. According to the specifications, you must verify that the voltage is at less 21V at the end of each line.
(Aug 16 '10 at 11:49)
cthulu
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You need all addresses if you use repeaters. I dont think its for future use /t |
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64 is related to the powerplay supply. If new devices consumes less it will of course be possible to add more |
