Sep 23


Finally an almost stable implementation of PSG audio chip SN76489 from TI and Cassette TAPE circuitry. This implementation of the PSG is not exactly the same as original, this one (named 'SN76490' by me...) doesn't slowdown the cpu including WAIT cycles, due to availability of a command FIFO inside the chip that speed up bus operations. The generated audio routes to the CODEC audio engine that drives the onboard Wolfson WM8731 chip as DAC and as ADC using the integrated LINE-IN. The tape signal is sampled, filtered and converted with a simulated Schmitt Trigger.

Last but not least, the PS2 keyboard connected to DE1 board, handles the SK1100 SEGA keyboard implementation, translating every keycode into SK1100 map.

The video shows every modules with a fully working tape loading stage.

Thanks to SC-3000 Survivors website and his founder Digimorf for the online tape programs and for incredible virtual SR-1000 TAPE loader!!!



Sep 19

This is my first beta version of the TMS9928 VDP Mode 2 implementation.
Sprites are not finished yet, so not included.
System main clock is 21,42857 Mhz (50 * 3 / 7) but VGA is running at 25Mhz.
A line-based buffering allows the clock synchronization.

SDcard loader are faster now using MasterClock / 2,
but it's track based and no FAT is supported yet.
The video shows the system startup 2 times in order to underline the new SD loader speed.



Sep 17


This time your eyes are pleasured by my first attempt to recreate SEGA SC-3000 home computer (1983).

Through this video you can see my IPL rom loading original SEGA BasicLevel 3A from SDcard.

After loading 32KB of data into RAM, the IPL rom deactivate itself rebooting into loaded data.



Sep 12

SDCARD! Finally an almost correct initialization.

On first row onto the screen we can see the initialization commands prefixed by ">" character.

We can see CMD0, CMD59, CMD8, ACMD41, CMD16 and finally CMD17 (READ_SECTOR).

The data is written onto sdcard starting from sector 0 using a sector-editor, in order to avoid (by now) FAT routines implementation.

The screen shows on second row the data from 0x0100 to 0x01FF (256 bytes) of SEGA BASIC Cart.




Sep 05

Textmode! 40x24, 240x192 pixels + borders. 6x8 chars.

The SC-3000 has CPU access limitations during display time.

The SC-3000X can access to VRAM during display area 1 time every char row.

VRAM accesses are done using ports $BE/$BF.