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Author Topic: Enterprise MIDI hardware (Read 1042 times)

Online gflorez

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Re: Enterprise MIDI hardware
« Reply #15 on: 2018.December.12. 23:36:01 »
What a good clue!

But, who is Jefrey?

Offline Zozosoft

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Re: Enterprise MIDI hardware
« Reply #16 on: 2018.December.13. 09:34:19 »
I'm interested about the output :-) Want to hear in a real life the musics what we found in one Paradise Software tape.
I talking about these:
http://enterprise.iko.hu/EPV1.MP3
http://enterprise.iko.hu/EPV2.MP3
http://enterprise.iko.hu/EPV3.MP3
http://enterprise.iko.hu/EPV4.MP3
http://enterprise.iko.hu/EPV5.MP3
http://enterprise.iko.hu/EPV6.MP3

Werner wrote about it:
Quote
I can't believe it !!!! The first song is definitely played by the ENTERPRISE and I think it was on a Roland MT-32. I will never forget this song, because it was the first one that Vilmos presented me in Munich. It is very much like something from Jean Michel Jarre and that is the reason, why I am remembering it so well. The others I cannot remember, but Vilmos had a wide collection of them.

Offline IstvanV

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Re: Enterprise MIDI hardware
« Reply #17 on: 2018.December.17. 14:32:11 »
I would love to have one of these MIDI interfaces, but the cartridge bay is better populated with a good SD-reader.

Cartridges also have the disadvantage that they do not support I/O ports. Memory mapped I/O is more problematic to emulate (unless it is somehow hacked into the existing SD card interface), and it would be slower to read in a modified version of midiplay, because paging needs to be saved, changed and restored in a high frequency IRQ handler. Assuming it is based on the 6850, input could be implemented better if the interface supported generating interrupts, otherwise the 6850 needs to be polled at a fixed high frequency, which does work, but uses more CPU time. With a VHDL implementation of the 6850, a minor optimization would be possible by making the data register return FFh when no new data byte is available.
« Last Edit: 2018.December.17. 14:35:55 by IstvanV »

Offline Zozosoft

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Re: Enterprise MIDI hardware
« Reply #18 on: 2018.December.17. 14:37:01 »
István! You already looked inside the Scoretrack. Can you made a memory map of the 'a' Studio cartridge?

Offline IstvanV

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Re: Enterprise MIDI hardware
« Reply #19 on: 2018.December.17. 14:53:19 »
I need to check for more details, but the ROM is on segments 6 and 7, and the 6850 ACIA is mapped to 3FF8-3FF9h on segment 7. It would be easy to change how and where the MIDI hardware is accessed, because it is only a few lines of code in the ROM. Initialization:
Code: ZiLOG Z80 Assembler
  1. .   C142  3E 07        LD    A, 07
  2. .   C144  D3 B2        OUT   (B2), A
  3. .   C146  32 F8 BF     LD    (BFF8), A
  4. .   C149  3E 16        LD    A, 16
  5. .   C14B  32 F8 BF     LD    (BFF8), A
07:BFF8 is the status/control register, and it is set to 1/64 clock (baud rate should be 31250 for standard MIDI, so 2 MHz input to the ACIA?) and 10 bits format (start bit + 8 data bits + stop bit, no parity).
Sending one byte:
Code: ZiLOG Z80 Assembler
  1. .   DCAD  F5           PUSH  AF
  2. .   DCAE  0E B2        LD    C, B2
  3. .   DCB0  ED 40        IN    B, (C)
  4. .   DCB2  3E 07        LD    A, 07
  5. .   DCB4  D3 B2        OUT   (B2), A
  6. .   DCB6  3A F8 BF     LD    A, (BFF8)
  7. .   DCB9  CB 4F        BIT   1, A
  8. .   DCBB  28 F9        JR    Z, DCB6
  9. .   DCBD  F1           POP   AF
  10. .   DCBE  32 F9 BF     LD    (BFF9), A
  11. .   DCC1  ED 41        OUT   (C), B
07:BFF9 is the send/receive data register. Bit 1 of the status register is high when data is ready to be sent. I did not find more MIDI hardware related code, so it looks like Scoretrack does not support input (recording or real time play on a keyboard).

Offline Zozosoft

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Re: Enterprise MIDI hardware
« Reply #20 on: 2018.December.17. 15:01:05 »
Thanks! More easy to make schematic when know what do it is :-)

Online gflorez

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Re: Enterprise MIDI hardware
« Reply #21 on: 2018.December.17. 19:21:04 »
Cartridges also have the disadvantage that they do not support I/O ports. Memory mapped I/O is more problematic to emulate (unless it is somehow hacked into the existing SD card interface), and it would be slower to read in a modified version of midiplay, because paging needs to be saved, changed and restored in a high frequency IRQ handler. Assuming it is based on the 6850, input could be implemented better if the interface supported generating interrupts, otherwise the 6850 needs to be polled at a fixed high frequency, which does work, but uses more CPU time. With a VHDL implementation of the 6850, a minor optimization would be possible by making the data register return FFh when no new data byte is available.

I think like you, better an external expansion card. We have all necessary signals there. And bus expanders are cheap to build.

On the MSX approach they seem to connect the MC6850 /IRQ pin 7 to Z80 /INT, but then, who knows the origin of the interrupt?. I think that what is needed is to implement another read-only port for the interrupt status.

Offline IstvanV

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Re: Enterprise MIDI hardware
« Reply #22 on: 2018.December.17. 19:47:20 »
A separate port for reading the IRQ status is not needed, this information is available on bit 7 of the status register. It would be useful to be able to trigger Z80 interrupts with the ACIA however, but not essential.

Another idea for a more efficient MIDI input routine is to make the receive data register FFh when a new byte is not ready to be read (no IRQ). But this may not be worth the increased hardware complexity. On the other hand, if the 6850 is not the original chip but a VHDL clone, then it could be a relatively easy change.
« Last Edit: 2018.December.17. 19:54:50 by IstvanV »

Offline pear

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Re: Enterprise MIDI hardware
« Reply #23 on: 2018.December.23. 10:12:14 »
Does anyone have a photo of the bottom side of the interface PCB ?

Offline Zozosoft

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Re: Enterprise MIDI hardware
« Reply #24 on: 2018.December.23. 11:49:39 »
Does anyone have a photo of the bottom side of the interface PCB ?
22407-0

Offline pear

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Re: Enterprise MIDI hardware
« Reply #25 on: 2018.December.23. 12:07:30 »
Thanks :)
Do you have a photo of the top side with removed ROM ?

Offline Zozosoft

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Re: Enterprise MIDI hardware
« Reply #26 on: 2018.December.23. 13:57:48 »
Do you have a photo of the top side with removed ROM ?
Not yet :oops:
This is my interface. It is have a additional hack, for simulating ROM from SRAM. (But not work properly, ROM contents always damaged...) My plan is restoring it to original version. I hope after Christmas will have some free time :oops:
22409-0

Offline pear

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Re: Enterprise MIDI hardware
« Reply #27 on: 2018.December.23. 14:35:20 »
Would it be possible to borrow this interface ?
I'm trying to recreate the scheme.
There are terribly many vias :(

Offline pear

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Re: Enterprise MIDI hardware
« Reply #28 on: 2018.December.24. 06:57:26 »
I will not read more from photos :(
I can guess, but it's easy to make a mistake.

Offline Zozosoft

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Re: Enterprise MIDI hardware
« Reply #29 on: 2018.December.24. 13:01:49 »
Nice! This is in Eagle? Can you send the file? I will add the remaining wires.