Subfamilies include the 8/16-bit H8/300 and H8/500, the 16/32-bit H8/300H and H8S and the 32-bit H8SX series, each with dozens of different variants, varying by speed, selection of built-in peripherals such as timers and serial ports, and amounts of ROM, flash memory and RAM. Built-in ROM and flash memory tends to range from 16 KB to 1024 KB, and RAM from 512 B to 512 KB.
The basic architecture of the H8 is patterned after the DEC PDP-11, with eight 16-bit registers (the H8/300H and H8S have an additional bank of eight 16-bit registers), and a variety of addressing modes.
Both H8/300H and H8S have eight 32-bit registers, each of which can be treated as one 32-bit register, two 16-bit registers, or two 8-bit registers, with the H8S having an internal 32-bit configuration.[2] Several companies provide compilers for the H8 family, and there is a complete GCC port, including a simulator. There are also various hardware emulators available.
The family is continued with the H8SX 32-bit controllers.