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Posts: 79 | Thanked: 719 times | Joined on May 2014 @ Buenos Aires, Argentina
#3
Everybody loves diagrams. Please let me introduce a new one:

http://neo900.org/stuff/neo900-block-diagram.pdf

This block diagram is our current working draft for the specification of the next prototype, called GTA04b7v2.

Before I describe what it shows, a quick disclaimer: few things in there are truly fixed. Where we mention part numbers and such, this is meant to indicate what we currently think can do the job and generally looks nice. But we may still discover that it doesn't work, that it's not so nice after all (e.g., hard to source), or we may find something we like even better.

A quick explanation of what the colors mean: the background color of a box shows the origin of the part or subsystem design: light "gold" is from GTA04A4, darker "gold" is an earlier version of GTA04b7, be it the v0 or v1 prototype, or the pre-reorg v2 design. Yellow indicates some other origin or something we do from scratch.

A red background marks things we're still working on or where we will decide later what to do.

The frame color indicates what is to happen with the part or subsystem: black means that we keep the existing design. Red means that we change something or that the whole item is new in the v2 prototype.

A light blue frame indicates that the part or subsystem will not be implemented in v2 but has to wait a little longer. For example, v2 will not have its own CPU and memories because this would drive the PCB cost up. Instead, we plan to attach an external CPU board to drive things.

Inside or near each box is the name of the subsystem and the part number(s) of the principal chip(s) we think of using. Note that this block diagram is far less detailed than real schematics and there will be many more smaller support chips and an army of passive components in the real circuit.

The lines connecting boxes are signals or buses. They're labeled with tentative signal names or a very short description of what they do. Since I2C plays a very important role in this design, these buses are drawn in blue, to make them easier to spot. Assignment of devices to I2C buses is somewhat arbitrary and may change.

A dashed line indicates a connection we're not yet sure we want to make. The invisible connection means that the part is just there for mechanical testing. Did you spot it ? It's for the backup battery, which will actually become a "supercap".

The small numbers are not pin numbers but show how many signals the line contains.

There also plenty of question marks to indicate parts and other details that still have to be chosen or defined.

For future reference, this is what the diagram looks like at the time of writing this post:
http://neo900.org/stuff/werner/web/g...2014070921.pdf

The link at the beginning points to whatever is the current version, which will be updated as we progress.

- Werner
 

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