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There are a number of settings on the smart packet radios boards which can be changed at any time during operation. These include, but are not limited to, the slot time, and the limit of the exponential back-off. Changing many of these settings are self-explanatory, just key in the correct instruction with the desired change. However, changing the slot time is slightly different. Due to inconsistencies in the timing of some functions, it was difficult to implement an accurate way to adjust the slot time to any given value. Instead, it was decided that an array of pre-determined slot times would be stored on the MCU, and that the host terminal would select from that array. At present, the array can cause the slot time to be 0, 15, 30, 45, 60, 75, 90, 100, 150 or 200 ms, and selection takes place in the form of an index to that array. For example, to select a slot time of 60ms, one would input 4 in the instruction, as the index of 4 corresponds to a slot time of 60ms. A full list dynamic settings is given in Table 2 below.

Variable Header Code Description
Enable/Disable MAC sub-layer 0x04 Write a '1' in the instruction payload to enable the MAC sub-layer, or write a '0' to disable the MAC sub-layer
Source Address 0x08 Writes the first byte of the instruction payload as the source address
Slot Time 0xB3 Takes the first byte of the instruction payload and uses it as the slot time index (as described above)
Back-off Limit 0x80 Takes the first byte of the payload and writes it as n in 2n 1, which is the maximum number of slot times to wait before retransmission.

Table 2: Table of variables which can be dynamically allocated

-- XiaohongWu - 2012-01-31

Topic revision: r1 - 2012-01-31 - XiaohongWu
 
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