Placing Objects on the Schematic

Placing Objects on the Schematic:

Having selected the parts we need the next thing is to actually place them on the drawing area – the Editing Window – and wire them together. You’ll notice from the screenshot that we have also split the contents of the schematic into logical blocks of circuitry. This is partly aesthetic but also reduces wiring clutter on the schematic and will allow us to cover the use of terminals to form connections as we work through the tutorial.

The Main Street of the dsPIC Data Recorder schematic
The Main Street of the dsPIC Data Recorder schematic

 

We are going to start off simply and complete the block of circuitry comprising the I2C Memory device as shown below:

I2C circuit section
I2C circuit section

Begin by placing the I2C memory device as follows:

  • Select the 24CL64 device from the Object Selector.
device from the Object Selector
device from the Object Selector
  • Left click on the schematic to enter placement mode.

click on the schematic to enter

  1. Move the mouse to the desired location for the part.
  2. Left click the mouse again to ‘drop’ the part and commit placement.

again to ‘drop’ the part and commit placement

Often we need to move parts or blocks of circuitry after placement and now is a good time to cover the different ways in which we can do that. The procedure for this should be familiar to most users; we need to select the object(s) we want to move, left depress the mouse, drag to the new location and finally release the mouse to drop.

We can select an object in ISIS in several ways as detailed below:

  • Choose the Selection Icon and then left click on the object. This is a standard technique found in most graphical applications and will tag any object. Bear in mind when using this technique that you must change back to component mode for example, when you wish to perform other actions such as placing components etc.
  • Right clicking the mouse on an object will both tag the object and present a context menu containing available actions on that object.
  • Draw a tagbox around the object by depressing the left mouse button and dragging the mouse to form a box encompassing the object to be selected. This method will work for any object (or indeed sets of objects). Sizing handles are provided to allow you to resize the tagbox in the event that it does not fully enclose the object. This is the technique that should be used for moving multiple, connected objects or blocks of circuitry.

We’ll get plenty of practice moving things around as we lay out the schematic; for now just use one of these techniques to move the memory device down towards the bottom left of the Editing Window in roughly the same position as in the screenshot at the top of the section.

Having placed the memory device, we now need to get the peripheral circuitry down and oriented correctly. We are going to need two 10k pull up resistors and two 100 Ohm resistors for the data and clock lines. Additionally, we are going to need to use terminals to achieve connectivity with power, ground and other sections of circuitry. Begin by selecting the CHIPRES10k device and click left once on the anti-clockwise Rotation icon (shown below); note that the preview of the resistor in the Overview Window shows it rotated through 90°.

Rotating the CHIPRES10K
Rotating the CHIPRES10K

Now place the resistor above and to the left of the memory device in the same way as before. Then, simply left click again on the Editing Window to start placing the second 10K resistor just beside the first one.

Next, select CHIPRES100R, rotate appropriately (see above) and place two to the left of the memory device in line with the SCK and SDA pins.

You can also rotate parts ‘live’ when in placement mode. Left click the mouse once to enter placement mode (at this point you will see the component outline following the mouse) and then use the ‘+’ and ‘-‘ keys on the numeric keypad to rotate the component as you are placing it. Left click again to commit the placement in the normal way.

We use terminals in schematic design simply to terminate a wire and assign a connection. Often this connection is to either power or ground but it can just as easily be to another wire elsewhere on the circuit. Terminals allow us both to vastly reduce actual wiring (avoiding spaghetti schematics) and to make connections between different sheets on the schematic. To place terminals, start by selecting the terminal mode; this will switch the Object Selector and provide us with a listing of the available terminal types.

Select the Terminal Mode Icon and then the required terminal
Select the Terminal Mode Icon and then the required terminal

We need a power terminal, ground terminal and also two default terminals for the connections on the I2C bus. From this stage, placement and orientation are identical to any other object in ISIS and should now be quite familiar. Place the appropriate terminals in their approximate locations now, such that the area around the memory device now looks something like the following.

Having placed the terminals, it should look like this
Having placed the terminals, it should look like this

Unless you are fairly skillful, you are unlikely to have got all the components oriented and positioned entirely to your satisfaction at the first attempt, so now is a good time to practice moving things around as discussed earlier. In particular note that yoju can drag a tagbox around a group of objects to move the lot in one go.

Tagging a section of the schematic
Tagging a section of the schematic

Similarly, you can clear a selection (or group of selections) either by left clicking in empty space or by right clicking in empty space and choosing the Clear Selection option from the resulting context menu.

Removing a selection area
Removing a selection area

Remember that you can rotate while moving by using the ‘+’ and ‘-‘ keys on the numeric keypad.

#collected from the proteus>>help>> tutorial page

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