Hi,
I know that this thread is very old, but please bear with me...
Recently, I got hold of a Philips :YES and have been able to successfully boot DOS Plus and MS-DOS from floppy. Unfortunately, I only have the machine itself, no documentation or disks. While the 3.5" DD drive I have is very picky about the disks it likes to read, regular HD drives do not work. I assume this relates to the disk-change/ready signal, but have not looked at it in detail yet. My machine seems to contain a revision 1 mainboard.
This machine is not PC compatible, but somewhat close. An MS-DOS 3.10 disk exists on the internet and boots on my machine. I have extracted the BIOS image (which is 64 KB in size and located at F000:0), and have started to reverse engineer some parts of it. The two chips carry a Digital Research sticker, but it seems to be mostly code. There is a third ROM chip with a Philips sticker, but it is not mapped into the address space.
Looking at the boot sequence, I did not see any way to boot DOS Plus from the BIOS ROM. The startup code will attempt to boot from the following devices in order: drive 00h (first floppy), drive 80h (hard drive), 01h (second floppy). If those fail, it will try to boot from ROM space at E000h:0, D000h:0, and F000h:0. That last attempt always succeeds: It initializes the video system and shows the "please insert disk" screen.
There are the following connectors on the back:
- two RCA outputs for audio and video
- a DIN-connector (7 pin) for the serial port
- a connector taking an edge connector, 2x20 pins - probably the printer port
- a connector taking an edge connector, 2x17 pins - probably for external floppy drives
The front side contains two 3.5" full height drive bays and a cartridge slot (takes edge connector, 2x22 pins). Unfortunately, I don't have any cartridge. Inside the case, on the left side below the mainboard, is another slot (takes edge connector, 1x12 pins). I don't know what this was used for. The backplane connector contains 3x32 pins.
A regular, 5-pin DIN connector gets access to the Rx, GND, Tx, P16 (on MUART chip) and CTS signals. The BIOS will initialize the serial port to 1200N8, but can definitely run at 9600 bps. The chip should support 19200 bps, but I have not tested this.
If anyone has some documentation about this system, I would like to learn more about it.
Best Regards,
Svenska