|Home||S-100 Boards||History||New Boards||Software||Boards For Sale|
|Forum||Other Web Sites||News||Index|
Microsoft convinced some of Japan’s largest consumer electronics and computer manufacturers (Sony, Toshiba, Pioneer, Hitachi, and Yamaha) to license its technology to build MSX machines. This was a time when Commodore, Atari, Mattel, Coleco
and Radio Shack, even Apple, were flooding the US market with cheap 8 bit home computers.
The MSX standard was built around an 4Mhz, 8-bit Z80A CPU, and included other popular, and cheap components. In particular the Texas Instruments TMS9918A video chip and the General Instruments AY-3-8910 programmable sound chip. Standard configurations included 16K, 32K or 64K of RAM, BASIC and a BIOS in 32K of ROM, along with 16K of video RAM. All systems had a version of BASIC, MSX BASIC, which was quite good allowing easy programming access to the computer’s sound and video capabilities.
However the systems were cassette and cartridge based to load programs.
Once the IBM-PC disk based systems caught hold these MSX based systems lost
momentum in the US. In Japan and Europe however they developed a loyal
following and support. Indeed a 16-bit the MSX II (1985) and MSX II-Turbo
(1988) standard was announced.
In 2001, Kazuhiko Nishi initiated a 'MSX Revival' around an official MSX emulator called MSXPLAYer. This was claimed to be the only official MSX emulator at the time. All MSX copyrights are maintained by a group called the MSX Association. I seems to have gone a number or rearrangements and owners.
Today the main difference between the MSX and its contemporary counterparts is the presence of a very well-developed hardware abstraction layer implemented as the MSX-BIOS. This BIOS is structured to provide device independence and instant plug & play with zero user intervention to use the system.
A number of early Z80 based video games first originated in these MSX systems. For many it was their first exposure to computer programming. A number of people suggested we do a S-100 video and sound board to allow these programs to run is an S-100 system.
The V9938 Video Chip
The S-100 VDP will contain all the circuitry necessary to generate tan MSX style video display. It appears to the S-100 bus Z80 as two I/O ports called the Data Port and the Command Port. Although the VDP has its own 16 KB of VRAM (Video RAM), the contents of which define the screen image, this cannot be directly accessed by the Z80. Instead it must use the two I/O ports to modify the VRAM and to set the various VDP operating conditions. The VDP video chip we use is the Yamaha V9938 chip. It is similar to the Texas Instruments TMS9918A chip. The screen has 16 colors, and four screen modes. The resolution is always 256 x 192. It also has a sprite system which can control 32 sprites, with a maximum of four sprites on a single horizontal line. The I/O ports that address the chip on this board are completely configurable. I use the following I/O ports to communicate with the VDP.
Please note the 64 pins on the V9938 have a 0.75" spacing. The chip requires an uncommon 64 pin socket. Fortunately Digi-Key sells these sockets (#LA10242).
The V9938 video chip is capable of displaying in a number of graphic or text based modes. The maximum text mode is 80/24 lines.
Programming the chip is a complex process. The V9938 programmers manual which can be obtained here, will require many hours of studying.
The V9938 (and this board), can directly drive a Composite Video monitor, but more normally we use its output to drive a RAMDAC to produce EGA style video displays. For this we use Bt478 RAMDAC. This chip has a 256 X 24 color lookup table with triple 8 bit video D/A converters. Further information about this chip can be obtained here.
The board also contains an AY-3-8910/8912 Programmable Sound Generator (PSG) chip. This is an LSI chip that can produce a wide variety of complex sounds under software control. Its operation requires only a single 5V power supply, a TTL compatible clock, and a microprocessor controller. Its flexibility makes it useful in applications such as music synthesis, sound effects generation, audible alarms, tone signaling and FSK modems. The analog sound outputs can each provide 4 bits of logarithmic digital to analog conversion, greatly enhancing the dynamic range of the sounds produced.
The AY-3-8910 has two general purpose 8-bit I/O ports and is supplied in a 40 lead package. The I/O ports that address the chip on this board are completely configurable. I use the following I/O ports to communicate with the AY-3-8910.
This page was last modified on 05/14/2016