Renesas H8/Tiny Processors

The Renesas H8/Tiny Processors

“Everywhere you can imagine” claims the Renesas tag line. I have no reason to doubt it. While not perhaps as well known among hobby users as the PIC and AVR chips, there is no doubt that the H8 processors from Renesas (formerly Hitachi) are very widely used in industry.

The power and flexibility of this series of processors makes the arcane architecture of the PIC look positively ancient. Why anyone would struggle with having meagre amounts of memory in awkard sized chunks is a mystery to me. Only the introduction of the 18Fxxx series and their descendants made the PIC even remotely useful. Its only real asset for the hbyist is the ready availability of devices in a form they could easily use without recourse to surface-mount technologies.

The AVR is a huge step forward in friendliness from the PIC. However, it does seem quite difficult to get hold of small quantities. They are a bit of a treat after struggling with PICs. Not only do they have a simple linear addressing scheme, the architecture and instruction set are much easier to understand and program. Nevertheless, they are still 8 bit processors and that creates some constraints when you are dealing with some applications. For example, the inability to read a 16 bit value atomically in a control loop can mean that you will have to disable interrupts while reading and writing variables to ensure that they are not corrupted by interrupt service routines.

The H8/300 Tiny processors have a 16 bit instruction set and a nice linear address space used for both code and data (Von Neuman architecture) This makes them easier to program for in a high level language like C. pointers, for instance, can point to either code or data without any of the need for language extensions as would be required for the AVR or PIC.

Perhaps the main reason these processors are less well known among hobby users is that they are not available in an easy-to use DIP package that you can place on a bit of breadboard. Given the number of features to be found on even the most meagre of these devices, it is hardly surprising that the simplest package normally used is a 48 lead surface mount flat pack. An interesting, and useful exception can be found in the H8/3664, the founder of the H8/300 Tiny series. This is available in a 42 pin shrink DIP package. These have a lead spacing of about 1.78mm. Not much help you may think but it so happens that that is ideal for mounting them on 0.1inch (2.54mm) pitch prototyping board – so long as you mount them at 45 degrees. See the link on the left for details of a simple prototyping board made up this way.

For a more comprehensive look at the H8 processors, try the excellent article by Jeff Bachiochi available on the Circuit Cellar site:

Spotlight on Renesas H8 Family

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