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  • Author Author: Jan Cumps
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KiCAD 8: RX23E-B kit - LCD schematic (and using a bus)

Jan Cumps

I'm building a PCB for Renesas' RX23E-B microcontroller. In this post: the LCD pins. I'm also using a KiCAD bus for the first time since V4. It changed a lot.

image

The crossed-out resistors are "do not populate". These LCD signals use the same pin as other functions on the board. I don't really need the resistors, if I don't plug the LCD in. But they are just empty footprints. The cost can be neglected.

Using a BUS in KiCAD 8:

In early KiCAD, a bus didn't hold a lot of intelligence. It was a blue line where you could connect signals to. In newer KiCAD versions, this has changed. A bus has structure, and knows what signals it holds. It can be a combination of signals, or a range. In my case: both. The LCD bus holds 3 ranges of signals: 4 voltage pins, 4 communication pins, and 40 segment signals.

I first defined the bus in the schematic setup:

image

Then I routed signals from the microcontroller to the bus, and from bus to LCD connector. The wires are (have to be) labeled at both sides.

I used global labels to indicate those shared signals, because they are shared in other sheets of the design. Example: with the timer that I use for AC excitation:

image

  • in reply to Jan Cumps

    I think that's worthy of raising on the KiCad forum, in case there's a way (and if not, then a feature request). I too would like to use such a feature. For sure there's some effort involved to make the components that will be connected together will have their symbols created in that compatible fashion but it would be worth it for the clarity of the resulting schematic.

  • in reply to shabaz

    I don't think that KiCAD has support for it, but I'd like to see that a bank only has one pin (or a few pins) in a symbol. Maybe called bank14[0..xx], + some supporting pins. And the connection mechanism would be a bus instead of a wire ...

    Let's say that you have a RAM IC. The symbol editor requires you to draw all address pins and all data pins. Wouldn't it be useful if you could make a symbol with one address pin[0..4]; one data pin [0..15] and a few supporting pins like reset, write, latch, clock, power and ground? and that the data and address pins came out as a bus, with known signals?
    ADM's Vivado already shows memory that way in their block designs.

  • in reply to shabaz

    I can work with Renesas' style.
    I think that their style is not easy when you want to tell a story, explain particular aspects of a design.
    But they have a structure and system. And it works. 

    Most likely, the way they do it, matches the corporate EDA software package workflow, and needs less time (and creativity) to draw.
    I learn that by trying to draw an "organic" schematic, I spend a lot of time pondering, balancing. In an industrial setting, that may not be efficient.

  • in reply to Jan Cumps

    Think I much prefer the method you chose, to split up the symbol (although if they were just creating a simple breakout, then the symbol looking like the physical layout could make sense). Renesas boards seem to have a lot of configuration pads! One Renesas board I saw had them spread all over the board, and was very hard to locate the right ones.

    I never got around to completing this, but I split up a Spartan symbol in a similar manner.

    image

  • for reference: Renesas schematic style.

    The LCD connector:
    image

    The microcontroller (single symbol with all pins):

    image

    and the "patch bay":

    image