These where small computers, you could actually carry around with you, and use on the go. While most of them where glorified programmable pocket calculators, the PC-E220 came with 32KiB of RAM and a CMOS-SC7852 CPU, that was code compatible with the Zilog Z80A at 3.58 MHz. That made the CPU faster than an Amstrad CPC or other Z80 based machines of the time.

While the 144x32 dot-matrix display is not very well equipped for graphics, because it is divided into 5x7 cells, it can print a wide range of characters, and displays 24 characters in 4 rows. By the standards of a pocket computer, that was a lot.

In order to write and use machine codes, it would be handy, to have a handful of tools, that allow interacting with a computer in a more user friendly way.

Some of the tools I'd like to have:

Save and load machine language programs to tape without the need to assemble them first. A small BASIC program should be able to simply create an image of a given memory block should be able to achieve this.
While the PC-E220 has a built-in assembler, it lacks a built-in disassembler. The monitor program it has built in, is -depite it's name- nothing more than a memory monitor. It does a well enough job, but I'd like to have something more in the line of the Commodore C-128 monitor. This should be written in assembly itself, and no larger than 8K (which would already be huge for such a program.)