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The Hitachi H8 is a large family of 8-bit, 16-bit and 32-bit microcontrollers made by Renesas Technology, originating in the early 1990s within Hitachi Semiconductor. The original design, the H8/300, was an 8-bit processor that had a 16-bit registers and ALU that allowed some 16-bit operations. Two upgraded versions were introduced, the H8/300L that expanded the instructions to become a full 16-bit machine while being optimized for low cost, and the H8/300H which further expanded the registers to allow 32-bit operations and was optimized for low-power/high-performance roles. Many variations exist.

The entire line was sold to Renesas in 2003. Renesas continues to sell the designs as of 2023^[update], but only to existing customers. An administrator on the Renesas user community boards commented in 2011 that there are no plans for further development of H8 based products.^[1] H8 was supported in the Linux kernel starting with version 4.2 but support was removed in version 5.19.^[2]

For higher performance needs, Hitachi introduced their SuperH family of 32-bit RISC-like microcontrollers, which have largely replaced the H8.

Variants

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, interrupts^[3] 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 architecture, 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. Unlike the PDP-11 however, the H8 architecture employs big-endian byte ordering.

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.^[4] 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.

Applications

H8S may be found in digital cameras, the Cybiko handheld computers, some ThinkPad notebooks,^[5]^[6] printer controllers, smart cards, chess computers, music synthesizers^[7] and in various automotive subsystems. The LEGO Mindstorms RCX, an advanced robot toy/educational tool, uses the H8/300. Namco employed an H8/3002 as a sound processor for various games it made in the late 1990s, notably those using its System 12 architecture.