Most of the devices you will encounter will involve only a single element. That is to say that by placing one component object, you account for all the pins in the physical part. This is in contrast to a multi-element part like a 7400 for which you need to place four gates to account for all the pins.
To make a single element device
1. Place graphics objects to define the device body in the appropriate graphics style(s).
2. Place device pin objects to represent the pins.
3. Annotate the pins to assign types, names and numbers using any of the standard editing techniques (see Editing An Object on page 30) or the Property Assignment Tool.
4. Tag all the objects that comprise the device. Then invoke the Make Device command and assign any default properties.
These stages are worthy of further discussion:
Defining the Device Body
The device body is essentially the complete graphic for the device, excluding its reference designator and pins. Very often, it will just be a box, in which case you should simply select and place a graphics box of the appropriate size in the COMPONENT graphics style. For components with more complex graphics such as transistors, op-amps and so forth you can use any of the graphic objects that ISIS provides in whatever graphics styles are appropriate and perhaps editing the objects and assigning local, fixed values to some or all of the graphics style attributes.
It is important to think carefully about what graphics styles you choose for the graphics in the new component. In general most graphics will be placed with the COMPONENT style selected and the graphic objects will not need editing as they default to fully following this parent COMPONENT style. Occasionally, however, you will want part of the graphics of the new device to be ‘fixed’. For example, you may want the solid body of a transistor to always be filled, perhaps to black. In these cases it is appropriate to edit the graphic object after placement and uncheck some or all of the graphics style attributes and to set local values though where possible you should endeavour to leave as many attributes as possible following the parent, COMPONENT, style. Your other consideration should be how the graphic object placed will fit in to a schematic. For example, if you are designing an OPAMP you may wish to use short lines between the slope of the body and the base of power, compensation or some such pins in which case it is best if these lines are placed in the PIN style so that they look like part of the pin.
If you wish to define the origin for the device, you should also place an Origin marker at the appropriate point. If you don't specify an origin, ISIS will default it to the top leftmost pin end.
? See 2d Graphics on page 81 for more information about placing and editing graphics objects.
Placing the Pins
When making a device, you use the special device pin objects, available with the Device Pin icon selected to place each pin in turn. Several types of device pin are pre-loaded into the Object Selector when you first select the Device Pin icon, and further types can be picked from the symbol libraries as required. You may also define pin types of your own.
As you place each pin object, you need to be sure that it is oriented correctly. The blue cross that appears at one end of each pin object designates the connection point for the pin; the other should generally be in contact with some part of the device body.
? For further information about pin objects see Pin Objects on page 79.
Annotating the Pins
This third phase of the device creation process is probably the trickiest, and can lead to some obscure problems much later on in the design cycle if not carried out correctly. You have been warned!
Each pin can carry a pin name, pin number and electrical type. The latter is used for electrical rules checking, and also by the VSM simulators. The electrical type of pins must be correctly specified for DSIM primitives in particular.
You have two basic approaches available to you in annotating the pins:
? Edit each pin in turn (point at it and press CTRL+'E' is probably easiest), and proceed to edit its properties using the dialogue form.
? Use the Property Assignment Tool to assign to the PINNAME, PINNUM and TYPE properties of the pins.
In most cases, you will find it appropriate to use a mix of these techniques.
In assigning pin names and numbers, bear in mind the following:
? Do not create devices with several pins having the same name. If a part has several VCCs or GNDs, label them VCC1, VCC2, VCC3 or GND1, GND2, GND3 etc.
Similarly, if the part has several unused pins, do not name them all NC (Not Connected) but name then NC1, NC2, NC3, etc. In fact, NC pins are generally best omitted from the schematic entirely, unless you have good reason to do otherwise.
ISIS
Alternatively, you can specify several pin numbers for one pin name. For example, you could label a pin as VCC, and then enter the pin number as 1/14. This would create two pins numbered 1 and 14 when the design was netlisted for PCB design.
? In netlisting, if a pin does not have a name, ISIS will use its number when a name is required. If it has no number, ISIS will use its name when a number is required. If a pin has no name or number, ISIS will give it one according to the order of pin placement.
? If the device is going to be used as a parent in a hierarchical design, you must give its pins names and these names must correspond with the names assigned to logical terminals on the child sheet.
? To place pins with overbars in their names, , use dollar ('$') characters to mark the start and end of the overbar. For example RD/$WR$ would display as RD/WR.
In assigning pin types, the following table may be helpful:
Pin Type TYPE ID Example Uses
Passive PS Passive device terminals
Input IP Analogue or digital device inputs Output OP Analogue or digital device outputs Bidir IO Microprocessor or RAM data bus pins
Tri-state TS ROM output pins
Pull Down PD Open collector/drain outputs Pull Up PU Open emitter/source outputs
Power PP Power/Ground supply pins
If you are unclear how to actually perform the required editing operations, the following sections of the manual are also relevant:
? See Pin Objects on page 79 for a full discussion of the Edit Pin dialogue form.
? See The Property Assignment Tool on page 53 for examples of how to use the Property Assignment Tool.
Invoking the Make Device Command
The final stage of creating a single element device is to tag all the objects (graphics and pins) which comprise the device, and then invoke the Make Device command from the Library menu.With a simple, single element device, no pinout script is required so you should leave this box unchecked.
The Edit Properties button invokes a separate dialogue form which allows default property values and types to be defined. See page 58 for more information.