Jump to content

nippur72's Photo


Member Since 13 Jan 2012
OFFLINE Last Active Today, 3:26 AM

Posts I've Made

In Topic: Any info on Video Technology Laser 500 computer?

Tue Nov 6, 2018 7:24 AM

@Bonstra do you know whether the ROM disk routines use any RAM memory locations apart from the relocatable disk buffers? I'm trying to assess if they can be reused in a CP/M setup where all the 4 banks would be mapped to RAM. So I need them to be "sandboxed" and not write in RAM other than the buffers.


In Topic: Any info on Video Technology Laser 500 computer?

Mon Nov 5, 2018 11:07 AM

cool! another two little secrets we discovered about this machine!!!


So the keyboard is customized via hardware, which makes sense because if you want make layouts 100% compatible and not rely on ROM for decoding. The ROM routine reads from mapped I/O: rows are on the address bus and columns on the data bus. The extended key works a little different because they added them later and they were out of address lines. The Laser 350 was meant to fit in a 310 case without the extended keys ( indeed you can move the cursor via [CTRL]+[M] [,] [.] [space] as in Laser 310).

In Topic: Any info on Video Technology Laser 500 computer?

Sun Nov 4, 2018 10:39 AM

On my Laser 500 peritel (French variant), the straps for CGA11 and CGA12 are inverted; CGA11 is always 1, and CGA12 is the opposite of GT.

I remember I did test the GT output. It outputs 0 in text mode and 1 in graphics mode (I don't remember exactly which modes I tested, must be GR0 or GR1).


do you have any clue what the GT signal does? It might be related to the data contained in the second charset (CGA12=0, CGA11=1). It's not an actual charset but contains all binary numbers repeated 8 times. E.g. at the position of character n. 23 it's the number 23 repeated 8 times. Maybe the use it as a sort of indexing in graphic mode, but I don't see why they had to add this over complication. 

Another question: do you have a QWERTY layout on your keyboard? And if you have a different one (QZERTY or perhaps AZERTY) do you know how the machine is able to handle the different layout? Is that done in hardware or via software using a different ROM ?

In Topic: Any info on Video Technology Laser 500 computer?

Sat Nov 3, 2018 6:24 AM

We have the real charset ROM dump! Tonino Bisazza extracted it from a Laser 500 he was repairing.

We discovered there are two additional charsets, GERMAN and FRENCH with their relative special letters.

Apparently the choice of the charset is hardwired (see the circuit diagram lines CGA11 and CGA12) but there is also a pin named GT (graphic table?) coming out the video chip that is involved in the selection of the set (I don't understand how though). I wonder whether there is an undocumented feature that is able to switch the charset via software.



In Topic: Any info on Video Technology Laser 500 computer?

Wed Oct 31, 2018 3:29 AM

@Bonstra great about the bit level emulation, I forgot to tell that I have a C tool that converts from .dsk to bit level and vice versa (the bit level file format is called ".nic"). I used it to convert @deepfb disks for the emulator. You can find it attached.

To make FDC emulation even more accurate I think we need a global time counter (derived from clock) in order to take into account the spinning of the disk.

If I am not wrong: 300 RPM => 5 rps. One bit-level track is 8192 bytes (65536 bits) => 65536 / 5 = 13107.2 bits per second. 

Regarding the manual, @Hasan Batto from the facebook group has an english version and he said he's committed to scan it in the future (he already scanned the DOS manual).