Digital Circuit Emulator written in Java
Digital Circuit Emulator (DCE)
by Michael H. Riley
DCE stands for Digital Circuit Emulator. This program contains the code for emulating a large number of TTL (7400 series), CMOS (4000 series), and a number of other integrated circuits (chips). This program allows you to put together electronic circuits and test them without the need to hardwire the actual circuit. DCE also provides an excellent platform for learning Digital Electronics because experimentation is so easy.
DCE operates in one of two primary modes: EDIT and RUN. The program starts out in EDIT mode where you can place parts and wire them together. You can enter RUN mode through the "Circuit/Run" menu item. The "Circuit/Run" menu item is a toggle and it will switch between the two modes.
The edit mode is used to build your circuit. In this mode parts can be placed, wires connected and digi-scope probes attached or removed.
The run mode is used to simulate your circuit. In this mode all of the parts will become active and some will become interactive.
NEW - This command will erase the current circuit.
LOAD - This command will allow you to load a previously saved circuit. A file access box will be displayed on the screen show ing the available circuit files.
SAVE - This command will allow you to save the current circuit. The SAVE command will save to the last file either opened or saved. If no file has been opened or saved, then it will ask for a file name for saving.
SAVE AS - This command will allow you to choose a file to save the current circuit. The file access box will be displayed and selection of a save file can be performed.
RUN - This command turns on the power to your circuit. The circuit will be flipped right-side up and the RUN mode is started. See the section on RUN mode for operation of this mode.
STATUS - This command will show the current status of the circuit. How many parts, wires, and nets will be shown. The run statistics for the last run will also be shown.
CHECK - This command will perform several simple checks on your circuit. The purpose of these checks are to look for simple wiring errors.
SCOPE - This command turns on and off the digiscope. When the digi- scope is enabled, the traces for all connected probees will be displayed.
PART - This command is used for placing new parts in your circuit. When selected a menu of device groups will appear. All the devices in DCE are placed together in common groups. Select the group you require and the menu will be replaced with all the parts available in that group. Click on the part you need and the menus will go away and the cursor will change to a picture of a hand. Click on the hole where you want to place the chip. The hole that is selected is where pin 1 of the device will be placed. When placing custom chips, the file access box will appear with the names of all the custom chips that are available, select the chip you wish to use and then the cursor will change to the placement cursor.
DATA - This command brings up the parts menu for accessing on- line data sheets. This menu works exactly like the PART function menu. When a device is selected the data sheet for the part will be displayed on the screen.
WIRE - This command allows you to change the color in which wires are drawn.
When any pin of a placed part is clicked, a menu appears allowing you to select options for this part as described below.
ADD WIRE - This option allows you to connect a wire from the selected pin to another pin. When selected the cursor will change to a hand. Click on the other pin you want to connect the wire to.
CUT WIRE - This option allows you to remove a connection on the selected pin. When selected the cursor will change to a cross. Click on the pin on the other side of the wire to remove the wire.
MOVE PART - This option will allow you to move an already placed part. When selected the cursor will change to the hand cursor. Click on the hole where you want to move the chip to.
DELETE PART - This option will delete the selected part as well as all wires and probes conneceted to the selected part.
ADD PROBE - This option connects a digi-scope probe to the selected pin. Pins with digi-scope probes attached have their circles filled in.
REMOVE PROBE - This option removes a digi-scope probe from the selected pin.
SHOW NET - This command will re-draw the circuit board, but only show the wires that have a signal path to the selected pin.
SHOW ALL - This command resets the viewer to display all wires.
DATA SHEET - This command will call up the data sheet for the selected part.
The run mode flips the circuit board right-side up and then applies power to the circuit. In this mode switches can be manipulated and output can be seen if output devices exist in the circuit.
While a circuit is running any switch can be changed just by clicking on the switch. Buttons will remain pressed only as long as the mouse button is held down over the button. Dip switch settings can also be changed. Note: Dip switch settings will always remain in the state they were last set. When a circuit is saved, any dip switch settings will also be saved.
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You do not need to connect the GND or VCC connections of any chips. These connections are placed on an internally used Net. You also cannot get power from these pins, If you need GND or +5v then place a power-supply part.
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Due to the way that wiring nets are resolved you must be careful how you use switches. Technically switches do not have inputs and outputs, but in DCE the wiring nets only work with inputs and outputs, therefore the switches have been altered to work with DCE's wiring scheme. On a switch, the inputs will have SQUARE pins while the outputs will have the usual CIRCLE pins. The normal position of a switch is indicated with a line going between the center pin and the normal pin.
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LEDs have a line located near the Cathode (-) end. Both leads of an LED must be connected for the LED to work. Pin 1 of an LED is the cathode.
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Unlike previous versions of DCE, the anode connection of the TIL311 and MAN10A parts must be connected for the LED portion of the part to function.
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The 74LS47 has a peculiar mode when it comes to this simulation. If you use the RBI then you must have a connection on the RBO/BI connection for proper operation. If you do not make a connection here, then when the display is blanked, it will not unblank.
In this tutorial we will build a simple circuit. First we need to learn about pin numbers so that wires can be properly connected. On all chips there is a small dot near pin 1. When in the edit mode, this dot appears in the upper left corner of the chip because the chip is being viewed from below. In the run mode, the dot appears in the lower left because it's viewed from above. The pin numbers then move along the same side of the chip. Pin 2 will be just to the right of pin 1. When we get to the end we move to the opposite side of the chip and start moving leftwards assigning pin numbers. Below is a sample chip showing the pin numbers from both top and bottom views:
8 7 6 5 1 2 3 4
| | | | | | | |
+-+--+--+--+-+ +-+--+--+--+-+
| | | • |
| • | | |
+-+--+--+--+-+ +-+--+--+--+-+
| | | | | | | |
1 2 3 4 8 7 6 5
Top View (Run Mode) Bottom View (Edit Mode)
The two display chips (MAN10a, and TIL311) appear vertically on the screen and the pin 1 will appear in the lower left on these chips in the edit mode. On switches (but not DIP switches) pin 1 is towards the top in the edit mode. DIP switches are numbered the same as chips.
Now lets build a circuit. Just follow the steps below:
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Pull down the PARTs menu and select 'GATES'.
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Select the 74LS08 (third from the top).
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The cursor will change to a hand or a small picture of chip with a small arrow pointing upwards to the left. This is called the placement cursor. Click on a hole near the middle of the screen and a 74LS08 part will appear on the screen. Look for pin 1, remember it is in the upper left corner of the chip and is marked with a white dot.
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Pull down the PARTs menu and select 'SWITCHES'.
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Select the 'SWITCH SPDT 2-IN 1-OUT'. This is the second one on the list.
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Place this part about 6 or 7 holes below the 74LS08. Take a close look at this part. Notice in the center there is a round pin and above and below there are square ones. In DCE the round switch pin represents the output from the switch and the square ones represent inputs. Also note that there is a line connecting the center pin with the square pin on the top. This line represents the normal position of the switch (the position the switch is in when the circuit is turned on).
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Get one more of the same switches and place it below the 74LS08 and about 5 holes left or right from the first switch.
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Pull down the PARTs menu and select 'POWER SUPPLY'.
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Place the power supply part to the left of the 74LS08. Notice that near one pin of the power supply there is a minus (-) sign, this represents the ground pin of the circuit. Next to the other pin is a plus (+) sign, this represents the +5v supply.
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Pull down the PARTs menu and select 'OUTPUT DEVICES'
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Select any color of LED. and place it directly above the 74LS08 about 6 or 7 holes away.
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Pull down the WIRE menu. This menu lets you change the colors of wires. Select black. We are going to place some ground wires, which are typically black.
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Click on the negative pole of the power supply (the one with the minus sign). A menu will appear. Select 'ADD WIRE'. The cursor will now change to either a picture of a soldering iron or possibly a hand.
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Click on pin 1 of one of the switches (remember pin 1 on switches is towards the bottom of the screen in Edit mode). A black wire will be drawn between the power supply ground terminal and the switch.
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Now connect pin 1 of the switch above with pin 1 of the other switch.
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Now connect a wire from the negative power supply to the cathode of the LED. The cathode can be identified by a small line that appears closer to the top pin. Therefore the wire should be connected to the top pin.
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Pull down the WIRE menu and select RED. We are now going to add some positive power connections which are typically red.
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Place a wire between the positive pole of the power supply (the pin with the plus sign) and pin 3 of one of the switches. Pin 3 will be the pin towards the top of the screen in Edit mode. Remember pin 1 was on the bottom.
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Connect pin 3 of the switch above with pin 3 of the other switch.
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Pull down the WIRE menu and select BLUE.
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Connect a wire from pin 2 of one of the switches to pin 1 of the 74LS08. Remember pin 1 of the 74LS08 is marked by a white dot.
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Connect a wire from pin 2 of the other switch to pin 2 of the 74LS08.
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Connect a wire from pin 3 of the 74LS08 to the anode of the LED. Remember the cathode was the pin with the line near it which appears towards the top of the screen, therefore the anode is the pin towards the bottom of the screen.
This circuit is now completed. Turn the power to the circuit on by using the CIRCUIT/RUN menu option. The circuit board will now be flipped right side up. Both switches will be in the down position and the LED will not be lit.
Turn on a switch by clicking on the white part of the switch. The switch will change to the up position, the LED will still be off. Now turn on the other switch and the LED will turn on. In this circuit the LED will only light when switch 1 AND switch 2 are in the ON (or up) position. This circuit is therefore called an AND gate.