Find the latest Issie release. At the bottom of the page, you can find the latest pre-built binary for your platform (Windows or ARM64 Macos). Issie will require in total about 200M of disk space.
Issie.exe
application in the unzipped files.Once you open Issie you should see two options: New Project
and Open Project
.
New Project
Create Project
This process creates a folder where your project will be stored and the first sheet of your project, called main
. You can see this by clicking at the Sheets
selection button.
Let’s start with a very simple schematic: a simple 2-input AND gate.
Add the following components to your canvas from the Catalogue
tab:
INPUT/OUTPUT
=> Input
=> Name: ‘A’, Bits: 1INPUT/OUTPUT
=> Input
=> Name: ‘B’, Bits: 1GATES
=> And
INPUT/OUTPUT
=> Output
=> Name: ‘OUT’, Bits: 1Now make the appropriate wiring to connect all the components by clicking on one port and dragging the wire to the port you want to connect it to. Connect:
Your design should look like this:
Time to simulate the design and see how the output OUT
changes as we change the two inputs.
Click the Simulation
tab which is located on the top-right corner and then Start Simulation
. Now you can change the value of the two inputs and see how the value of the output. Try all 4 combinations of inputs:
and check that the output is correct based on the truth table of the AND gate.
Well Done! You just completed your first ISSIE design.
This section will exploit the features of ISSIE to create clean and good-looking schematics when making bigger designs.
C
and D
each 1-bit.OUT
delete
button on your keyboardRESULT
Again, simulate the design and check the output remains correct as you change the values of the 4 inputs
The schematic here is not easy to read. Let’s improve it! The ISSIE canvas is fully customisable to allow the creation of readable and good-looking schematics. Specifically, we can:
You can view the shortcuts for all these modifications by clicking on the edit
and view
menus.
The improved schematic:
Catalogue
Menu we can find an extensive and complete library of components (gates, flip-flops, RAMs, ROMs, n-bit registers)In this section we will create a hierarchical design with multiple design sheets by using schematics as custom symbols in other design sheets. Here is the aim: The design we created earlier can be used in a larger design as a decoder of a 4-bit message to produce a true/false result. Therefore, we are going to create a schematic with an asynchronous-read 4-bit ROM using the schematic we created before as a custom symbol.
Steps:
main
to decoder
(Sheets -> rename)main
MEMORIES
=> ROM (asynchronous)
). Select 4 bits addressor, 4 bits data and the Enter data later
optionTHIS PROJECT
=> decoder
)INPUT/OUTPUT
=> Output
)INPUT/OUTPUT
=> Input
)SplitWire
components (BUSES
=> SplitWire
) separate the 4-bit ROM output to 4 1-bit wires. (see image below)It’s time to use a hidden part of the Issie UI to move ports on custom symbols. Issie allows you to re-order and change the side of input and output ports of custom symbols by CTRL
+ CLICKING ON THE PORT
you want to move. The UI, once you realise that you must keep Ctrl
(Cmd
on Macs) pressed, is intuitive.
Preview how it works in the gif below:
Currently our ROM is empty as we selected the option Enter Data Later
before. Let’s put some values in our ROM.
Properties
tabview/edit memory content
done
Issie also allows ROM and RAM initialisation via .ram
text files of hex data in the Issie directory. See the Issie Eratosthenes demo for an example of this. The memory component properties tab offers additional options when there .ram
files present.
Simulate your design! Change the value of the addressor input and see whether your decoder produces a true or false result for each number you assigned to the ROM.
Let’s now make our top-level design a clocked one using a counter to form a custom addressor that will increment every clock cycle. Uing the waveform simulator we will be able to view the output of our circuit for all memory locations. In order to create such designs easily, ISSIE offers a Counter
component which, starting from 0, increments by one every clock cycle. Note that counters also have options, under properties, to add a Load
or Enable
inputs.
Add a Counter
from the Catalogue (FLIP FLOPS AND REGISTERS
). Now select the component and click on Properties
. You can select to remove the load
and enable
ports and give them the default functionality (which is what we want in this case): enable=1; load=0;
Create a schematic like the one below:
As soon as you connect everything correctly, You can simulate your design. Click on Simulations
and then Wave Simulation
.
Start Simulation
buttonSelect Waves
AROM1.Dout[3:0]
REG1.Dout[3:0]
RESULT: DECODER1.RESULT
Done
hex
or bin
to make the waveforms more readableNow, keeping the simulation open, add an extra register between the counter and the ROM address (or make any other change you want) and check that the simulation has the expected output. You can see the changes in the waveform simulator by clicking the Refresh
button which will be enabled as soon as it detects a change in the schematic.
One of ISSIE’s features is the ability to view the truth table for a small combinational circuit.
Simulations
and then Truth Table
DECODER
componentGenerate Truth Table
button on the ‘Truth Table for selected logic’ sectionRemove Redundancies
You can also select your inputs to be algebraic values to get an expression for each of your outputs.
Back to full table
Algebra
Last but not least, ISSIE allows you to create combinational custom components by defining the logic in Verilog. Click on Verilog
-> New Verilog Component
(Catalogue) and write the logic of your decoder in Verilog.
Save
Verilog
section in the Catalogue)You now know how to use ISSIE to create & simulate digital designs.
You can now create your designs (from simple circuits to fully functioning CPUs) and either simulate them or extract them as Verilog to use them with other tools.
For inspiration, look when you start Issie under the demos option for eratosthenes demo which consists of an EEP1 CPU running an Eratosthenes Sieve program written in EEP1 assembly language.