Differences of device

Where can I find a summary of the differences among VR Series products?

See the following web page.
Click on a Series names listed at left or shown in the graphs or text to view a comparison chart.

http://www.necel.com/micro/english/product/vr/vr.html

What are the differences between the VR4131 and the VR4122 ?
I designed a CPU board using the VR4122, and I am currently investigating the changes that need to be made in terms of software when the CPU on that CPU board is changed as a result of switching from the VR4122 to the VR4131.

In terms of software, the VR4122 and VR4131 are compatible.
The VR4131 includes instructions that have been expanded from the VR4122.
The VR4131's CPU core differs from that of the VR4122. (The VR4131 has a superscalar pipeline.)
The peripheral functions of the VR4131 are the same as those of the VR4122, but the N-wire function has been deleted from the VR4131.
Also, the VR4131 is pin-compatible with the VR4122, but if a design featuring the VR4122 with no use of the N-wire function is created, there are two pins that are not pin-compatible with the unused pin handling method.

In cases other than when pin assignment has been added, I think the VR4310 can be used in the same way as VR4300-133.
Concerning changing devices, since I do not want to change the hardware design timing nor change the software, which cautions should I be aware of?

No changes are required.
The only specification change is that the DivMode setting has been increased from 2 bits to 3 bits.