Roo's Dreamcast Page

A 32/64/128 bit computer?

The SH-4 is a multiple bit CPU. Here is a list of the different functions, there bit sizes and the benefits of that particular bit size.

Function	Bits	Benefit
Instructions	16 bits	40 percent smaller size then comparable 32-bit RISC
CPU Precision	32 bits	More accurate results compared to 16-bit values
Memory Addressing	32 bits	4 GigaBytes memory access which is overkill for a console that will not have more then 32 MBytes of memory
External Data Bus	64 bits	800 MBytes/second transfer rate with 100 MHz SDRAM
Floating Point Precision	64 bits	More accuracy in mantissa portion of number which aids graphic operations
Floating Point Bus	128 bits	3.2 GBytes/second transfer rate from the data cache for matrix data aligned together as four separate 32 bit values like this: [32bit][32bit][32bit][32bit]

The Semiconductor Industry Association (SIA) bases its classifications for a CPU's bitness based on external bus sizes. The maximum width of the SH-4's external data bus is 64 bits, so the SIA would classify the SH-4 as a 64-bit RISC architecture. We classify the SH-4 as a multiple bit sized CPU where it uses multiple bit sizes for maximum advantage depending on the function of the CPU.

Software Modem?
The SH-4 has a special register called the floating point integer communication (FPIC) register. This register along with the two separate serial communication interface channels that are on the chip can lend themselves to providing a modem through software execution. If the SH-4 can provide a software modem with little overhead, then this would be a great way to give the Dreamcast communications ability at low cost. The SH-4 has the potential to provide a software modem with very little overhead because of the strength of it's floating point unit in doing multiply accumulates (MAC), which is a very important instruction in communications algorithms.
The many benefits to having a modem built into the Dreamcast:

browsing the internet
downloading extra levels, characters, vehicles for games
multiplayer gaming

These reasons listed above are also all excellent reasons to promote sales of the Dreamcast.

A company called RSA Communications, Inc. currently offers a software modem for the Hitachi SH-3 called Native Modem Technology. This software modem offers V.34, up to 33.6 kbps and also 56 Kbps. The SuperH series processors have such fast execution speeds that it is possible to run complicated modem algorithms concurrently with other application programs. RSA's NMT software can connect to a phone line with just a network interface module consisting of a Codec and a data access arrangement instead of a dedicated, power-consuming modem. The softmodem consumes much less power than dedicated modem hardware and takes up less real estate on a circuit board. RSA has successfully ported the software modem to Windows CE. The company plans to expand applications for the software to include SuperH processor based games, fax machines, multifunction peripherals (MFPs), and other products.

A design approach that combines a Hitachi SH-3 series processor and associated hardware components with RSA&rsquos NMT software eliminates the need for a separate dedicated modem module, thereby saving cost, space, and power. Hopefully RSA is porting their technology to the SH-4 for Sega's next generation console.

More information on Native Modem Technology (NMT) for the Hitachi SH series of chips can be obtained at RSA Communications, Inc. website.

(Note: SEGA is not using the softmodem technology from RSA Communications. This section will be updated at a later date.)

About Hitachi
Hitachi, Ltd.(NYSE: HIT), headquartered in Tokyo, Japan, is one of the world's leading global electronics companies, with fiscal 1996 (ending March 31, 1997) consolidated sales of $68.7 billion. The company manufactures and markets a wide range of products, including computers, semiconductors, consumer products and power and industrial equipment.