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Concept
Hitachi 6309
Summary
The 6309 is Hitachi's CMOS version of the Motorola 6809 microprocessor, released in late 1982. It was initially marketed as a low-power version of the 6809, without reference to its many internal improvements.
While in "Emulation Mode" it is fully compatible with the 6809. To the 6809 specifications, it adds higher clock rates, enhanced features, new instructions, and additional registers. Most of the new instructions were added to support the additional registers, as well as up to 32-bit math, hardware division, bit manipulations, and block transfers. The 6309 is generally 30% faster in native mode than the 6809.
This information was never published by Hitachi. The April 1988 issue of Oh! FM, a Japanese magazine for Fujitsu personal computer users, contained the first description of the 6309's additional capabilities. Later, Hirotsugu Kakugawa posted details of the 6309's new features and instructions to comp.sys.m6809. This led to the development of NitrOS-9 for the Tandy Color Computer 3.
The 6309 differs from the 6809 in several key areas.
The 6309 is fabricated in CMOS technology, while the 6809 is an NMOS device. As a result, the 6309 requires less power to operate than the 6809.
The low-power use also means it can be paused for up to 15 cycles as it does not have to constantly refresh its internal state. This is useful for direct memory access as it allows external devices to pause the CPU to release the memory bus, read or write small amounts of memory, and then unpause the CPU again. No other logic is required.
It is a dynamic design. The datasheet specifies a minimum clocking frequency and it will lose its state when the clock speed is too low.
The 6309 has B (2 MHz) versions as the 6809 does. However, a "C" speed rating was produced with either a 3.0 or 3.5 MHz maximum clock rate, depending on which datasheet is referenced. (Several Japanese computers had 63C09 CPUs clocked at 3.58 MHz, the NTSC colorburst frequency, so the 3.5 rating seems most likely).
Official source
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