|速度||最小||解決済み||修正済み||2010-02-10 06:45||2010-02-11 06:47|
mrdo - ミスターDo!
|詳 細||The driver for Universal's Mr. Do has the wrong speed for the CPU, sound and screen refresh rate.|
Reason: the schematics have the wrong crystal oscillator values.
Mr. Do uses 2 crystals, each for the video timing, and CPU / Sound speed.
In the schematics, the crystal for the video timing is 20Mhz and for the CPU/Sound 8Mhz, which is divided by 2.
On the real Mr. Do PCB (8201 revision), the values for the video timing is 19.6 Mhz and for the CPU / sound 8.2Mhz.
That means, the real values for the game are:
CPU: Z80 clocked at 4.1 Mhz.
Sound: 2*SN76489 clocked at 4.1 Mhz.
The change in the video oscillator frequency also affects the refresh rate.
|再現手順||Locate a real Mr. Do PCB and compare the oscillator frequencies with those of the schematics. On revision 8201 PCB, they will not match.|
|追加情報||I have included 2 photos taken from my ORIGINAL Mr. Do PCB which verify my claims. |
The board was not modified in any way. In fact, it would be quite hard to purchase the two oscillators, because the frequencies are so odd.
Note: this descripancy in clock speeds is most probably also responsible for the off-key music in Mr. Do Run Run.
|添付ファイル||MrDo_PCB.zip (2010-02-10 06:45)|