| Method of choosing a device
I think that there are various conditions of device choosing. On this page, I will introduce my choosing way.
The number of the macrocells with correspondence with the input/output pin
The correspondence of one register(D/T flip-flop) with one macrocell. The number of the whole macrocells
When making the circuit which controls a circuit outside like the latch register, the number of the macrocells with correspondence with the input/output pin becomes an important condition.
By this condition, I choose a 44 pin type or a 84 pin type.
There are few numbers of the needed input/output and when making a complicated circuit inside, I decide the kind of the device by the whole number of the macrocells. The mounting space
In case of XC9572-PC44, there are few macrocells correspondence with the input/output pin than with the whole number of the macrocells. However, because there are many whole numbers of the macrocells, it is the device which is useful when making complicated logic.
I select a device by the space which is possible to mount the CPLD on the printed board. When CPLD of 84 pins(The area of 37mm x 37mm is needed at the size of the socket) can not be mounted, it is sometimes possible to mount if arranging CPLD of 44 pins(23mm x 23mm) in the direction of the side.Besides, there are various conditions. (Operation speed, Consumption current ...)
When doing such a way, the signal among CPLD must be considered.
I will show the order which designs CPLD below. It is necessary to have a lot of tests such as the simulation in case of the complicated circuit. Because the circuit which I make isn't complicated, I make a test simple.
|Examine the condition of the system which uses CPLD and decide the function to make CPLD have.
|Creating the software to realize a function
Change made software into the logic information by the fitter.
(Simulate operation by the case)
|Write data in CPLD by the programmer.
|Confirm operation with the actual circuit.