I am looking at "address-only mode" packets vs "paged mode addressing" packets, and I'm trying to understand how a decoder distinguishes one from the other. The first 2 bytes for Address-Only are: 0111C000-0DDDDDDD. The first 2 bytes for Paged-Mode are: 0111CRRR-DDDDDDDD. RRR can have a value of 000 (in the case of Data register 0). Couldn't these 2 commands end up looking the same?
Yes but that's OK because Register 0 is the address anyway.
Unless you have a need to handle the earliest DCC decoders which had only register mode programming (no current ones, nor any made for YEARS now have had that limitation) you don't need to implement any of that.
That the first data bit of the 'address' packet is 0 isn't something that differnetiate the address packet from a register 0 packet, it's just a byproduct of the fact that address are only 7 bits, 1-127. To make matters worse, not all command station support the same address range. Lenz for example only handle 1-99, a holdover from their pre-DCC system where the display only had 2 LED digits so could only display 0-99. There always were 7 bits reserved for the field so other manufacturers expanded that to use the whole 1-127 range.
--Randy
Modeling the Reading Railroad in the 1950's
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