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Video Display Interface Board
The Sprite Color Graphics (SCG) board provides Sprite and Color Graphics from the TMS9918 Video Display Processor and sound from the AY-3-8910 Programmable Sound Generator chip. It is meant as a supplemental display for games and multimedia presentation. The board supports two joysticks and paddles.
Current Version: "002"
Manufacturing Files: :boards:ecb:scg:sgc-002_gerbers.zip
KiCAD Files: ecb_scg-002.zip
For information on prior board versions, see the Legacy Wiki SCG Folder.
The ECB-SCG was developed by Tom LeMense and Dan Werner.
Parts List - PDF
Parts List - XLS
The TMS9918 is an NTSC format chip. A PAL version of this chip is available (TMS9928A) but it is not totally compatible per the following from the datasheet.
"The TMS9928A/9929A VDP's are functionally identical to the TMS9918A except that the NTSC color encoding circuitry has been removed and replaced with luminance and color difference signals. The TMS9918A is pin-for pin compatible with the TMS9928A/9929A, except for three pins, the composite video output, the external video input and the CPU clock output. These pins are replaced with the Black,White luminance and composite sync (Y) output and two color difference pins, Blue (B-Y), and Red (R-Y) outputs, respectively. The color difference outputs allow the user to generate Red-Green-Blue (R-G-B) drive for direct color gun control, or composite video for use with NTSC or PAL video color monitor. However, to connect these three outputs to R-G-B or monitor requires additional R-G-B or encoder circuity"
So maybe that is something for the next iteration…
A 2Mhz crystal is specified for the sound chip clock but on board dividers can be configured to use a higher frequency crystal. Also common serial and colour burst frequency crystals can be used depending on your need for frequency accuracy and compatibility.
Low cost LM386 based amplifier boards can be use to finalize the sound output and can be found very cheaply on alibaba.com.
Capacitors C7 and C45 are not critical values and 33uF or 47uF should work as well.
<note>The default SCG board ID has been changed from 0x50 to 0x98. All of the software posted below has been updated for the new board ID. Please ensure your board has been configured for the new board ID if you use any of the software below.</note>
J20: Board ID / Base I/O Address
* 3-4: 0x40
* 5-6: 0x20
The base i/o address is determined by shorting the pins listed above such that the additive value of the unshorted pins is equal to the desired address. So, for the default base port address of 0x98, you would short pins 3-4 and 5-6. Pins 1-2, 7-8, and 9-10 would remain open.
J5: Sound Config
1-2: All channels merged onto channel C
3-4: All channels merged onto channel A
The sound chip drives a total of three audio channels (A-C). The center channel (B) is hard-wired to mix it's output into channels A & C (left & right). If you want to bridge all three channels to produce monophonic output, you can short pins 1-2 and/or 3-4.
5-7: Audio Oscillator / 8
7-9: Audio Oscillator / 2
* 6-8: Audio Oscillator
8-10: Audio Oscillator / 4
You must short one (and only one) set of pins above. These pins allow scaling the audio chip oscillator input. The default configuration is no scaling with an osciallator frequency of 2.0MHz which is the maximum frequency allowed by the AT-3-8910 chip.
JP1: TEST2 Enable
Shorting 1-2 will ground the TEST2 pin of the sound controller, otherwise the pin will be disconnected. You would normally leave this jumper open. The AY-3-8910 datasheet does not document the functionality of the test configuration.
J21: Interrupt Enable
Shorting J21 will enable vertical blanking interrupts to the /INT line of the host CPU. You would generally leave this jumper open unless the software being used needs it. Note that the MSX software requires this jumper to be shorted.
J1: Video Output
1: External VDP Input
2: External VDP Input Sync Input
3: Color Burst Freq Clock Output
5: Composite Video Output
8: Composite Video Output (amplified)
10: Composite Video Output (amplified)
J18: Joystick A
2: Button 1
8: Botton 3
9: Button 2
J19: Joystick B
P1: Video Output (RCA)
1: Composite Video Output
J9: Audio Output
3: Right Channel Audio
4: No Connect
6: No Connect
8: ACR5 General Purpose TTL Output
9: Left Channel Audio
RV12: Left Channel Audio Output Volume
RV9: Right Channel Audio Output Volume
<note>The left channel and right channel trimpot's are wired in reverse direction and will need to be set at different positions for equal sound levels on each channel.</note>
The SCG board is not intended to be a general purpose terminal controller like the VDU, CVDU, and VGA3 boards. It does not have a keyboard interface and text output is limited to 40 characters per row. So, the typical way to use the board would be to add it to an existing system already running CP/M (RomWBW, UNA, etc.) and then run programs that utilize the graphics and sounds capabilities of the board. The MSX games and programs described below do exactly this. You start your system in normal CP/M, then run the MSX game/program desired.
RomWBW (v2.8.5+) provides support for text output to this board when TMS support is enabled. The board is accessed as the CRT device, so sending output to CRT: will work.
It is not possible to read from the CRT: device because the board has no text input capability. It is not necessary to have the TMS driver enabled in RomWBW to launch the MSX software – the MSX emulator below includes it's own driver for the board.
Two programs are available to test basic video operation of the card in the tms9918-test package. Refer to images below.
HW9918.COM will display the "HELLO WORLD" text on the screen.
TSTSPR.COM will display sprites and allow background colour changes.
Sound functionality can be tested with the ay-test package.
AY-TEST.COM will output a descending tone to each sound channel.
Note that the SBCV2 with the SCG card is not 100% MSX compatible. That said, there is enough compatibility and enough flexibility built into the MSX BIOS that some cartridge ROMS will work fairly well. In the zip file there is a selection of MSX cartridge images that do work with the SBCV2 and SCG card, but please make note of the following:
The AY-3-8910 is a widely supported sound chip and there is a large library of sound files that can be played on this board. Included in ROMWBW is a sound file player called TUNE which can play Protracker 2/3 and .MYM format PSG files. A collection of demonstration files is also included.