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ForumsSega Master System / Mark III / Game GearSG-1000 / SC-3000 / SF-7000 / OMV |
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SF-7000 replica
Posted: Mon Aug 15, 2022 11:17 am
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I resumed a project found on a french site and made a SF-7000 replica, but i get on boot only some weird screens and multiple but randomic beeps.
Since i noticed the original SF-7000 doesn't boot without the original 3" drive attached, i wonder if i missed some setup in the D8255AC ports that make fails the initial ROM check... there is some diag ROM or similar for further test? |
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Posted: Mon Aug 15, 2022 12:30 pm |
Did you refer to https://github.com/maxim-zhao/smsbioses/tree/master/SF-7000%20IPL for the IPL disassembly? Maybe that would help? Unfortunately I guess debugging into it will be difficult. | |
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Posted: Mon Aug 15, 2022 1:58 pm |
Thanks, i red the disassembly but it not seems useful for my case, the diag check ROM, RAM and VRAM.
I probably have an issue with /ROMSEL or the FDC... Anyone has changed the 3" drive with a 3,5" drive in the SF7000, and can confirm that it doesn't boot if the 3" cable is not connected, as i stated with mine when using the Gotek? |
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Posted: Mon Aug 15, 2022 10:59 pm |
Here are some instructions for replacing the drive with a 3,5" one: http://members.optusnet.com.au/spacetaxi64/MAIN/SEGA-SF7000.htm Although I haven't tried it. |
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Posted: Tue Aug 16, 2022 5:17 am |
In that guide (the only I found in the net too) is stated it's possible to completely remove the original floppy, but it's not true from my test (with gotek, not yet tried with a pc floppy drive).
I guess some of the PPI signals (/motor, /inuse, etc.) must be pulled low for initializing the FDD |
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Posted: Sat Oct 01, 2022 7:10 am |
If you need support, ask me. |
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Posted: Sat Oct 01, 2022 7:50 am |
Thank you, but i've already made great progress, thank to the help of @kamillebidan and the full schematics that @Bock published! I have to fix the rs232 part, and some stability issue, but i'm near the goal! |
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Posted: Sun Oct 02, 2022 4:00 am |
Nice to read it! |
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Posted: Sun Oct 02, 2022 11:57 am |
Hi, how do you fix the missing floppy issue? For ROM/RAM selection, have you used the 74LS32? |
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Posted: Sun Oct 02, 2022 12:49 pm |
Yes, the floppy issue was fixed... the SF-7000 Ground is connected via the external wire to the case, the case is connected to the floppy via a screw, and the floppy drive give the gnd to the sf-7000 motherboard via the 34 pin cable. So, if floppy cable is disconnected, the SF-7000 doesn't boot. I've added a wire from case to motherboad, and it works! For ROM/RAM selection, i use several logic IC, included a 74ls32 Here's the last schematic, it's not the final version but i hope i'm not far from it |
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Posted: Sun Oct 02, 2022 1:54 pm |
Nice, great to share your schematics. I did a cutoff version of it. Replaced memory selection and partial I/O logic with a PLD to reduce the number of components. I just removed serial and parallel IC/connectors inserting a CH376 USB interface which I will support instead parallel. Everything is still WIP. |
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Posted: Sun Oct 02, 2022 4:47 pm |
Great idea the pld to replace the original logic... and timing the RAM and ROM is really a pain running on the original schematics. Does it works fine, did you already made some tests? |
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Posted: Sun Oct 02, 2022 7:34 pm |
Yes, I did some test but I'd like to upgrade it to a real CPLD. As far as I know SC-3000 provides /MEMRD, /MEMWR, /IORD and /IOWR already merged with /MREQ, you can check it with a logic analyzer so, if you want to use it onnly on SC-3000, it not required to obtain /MEMR1 and /MEMW1. I don't know why it's present on SF-7000 original schematics. Second point: new EEPROM and SRAM (the IC I used on it at least) can accept /OE before /CE so probably you can avoid the latency added with 74LS04. My goal is to reduce as far as I can. When I will have a stable version I will share it. Using a 5V CPLD (like my EPM7064 can host at least other 3 IC). 74LS14 and 74LS06 can be necessary but I'm not sure. I handled a floppy drive with a simple Arduino as well as other microcontroller without any other chips. If you use a bigger EPM7128 probably you can put the 8255 logic used by SF-7000 into it. I will do other tests with HCT version of that IC instead the LS ones (taking in account that they can be faster). |
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Posted: Sun Oct 02, 2022 7:47 pm |
@kamillebidan (who is giving me a big help in adjusting my board) already made a "sf-7000 on a cart" using plcd and new hw, did you miss this post?
https://www.smspower.org/forums/18607-SF7000OnACartridge |
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Posted: Mon Oct 03, 2022 5:50 am |
Usually I do projects by myself for learning purpose. I can put everything in FPGA as well, or on an ARM like MCU, but it not my goal. Using oldskool 74LSxx IC is quite fun to understand how the Sega engineers did their job. Have you tested the serial port btw? |
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Posted: Mon Oct 03, 2022 5:16 pm |
That what i think too! ;)
It doesn't work, and no tx nor rd leds light. But i've made no further test, i'm waiting for a new pcb with less "floating wires" and (i hope) more stable system. |
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Posted: Tue Oct 04, 2022 4:53 pm |
Do you have an oscilloscope to test what's happening on the serial? |
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Posted: Thu Oct 06, 2022 12:48 pm |
Yes, without a scope and a logic analyzer I would not have made it this so far! |
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Posted: Sat Oct 15, 2022 6:45 pm |
Found some bugs and now i have a stable station, and serial works fine too, even at the "new" 19200 baud speed.
Waiting for new pcb batch for testing the new schematic that i hope will be the final version |
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Posted: Sun Oct 16, 2022 6:57 am |
19200 is very good! ☺️ |
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Posted: Fri Oct 21, 2022 4:14 am |
Hi, have you checked if the board layout you build, fit into the original case? I'm trying to make precise measurements to rebuild one. I'm doing servicing due to "beep" errors. Strangely I have 2 different errors on 2 different I/O carts: 1 beep on the original one (probably cable issue since I checked the UV EPROM), 2 beeps on my home made cart (dram isse?). Checking with oscilloscope I saw 4 of 8 dram chips (4164) with a a suspect waveform... |
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Posted: Fri Oct 21, 2022 7:32 am |
Hi, the pcb i designed has a similar form factor but it's smaller than the original one, and the rear connector and screw's holes are different. I've only one "filled" original SF-7000 case, so i'll place the new board in a black metal case 28cmx20cm. To make a perfect replacement board, it should be resized the pcb, repositioned the holes, and changed the power supply (now i use a 5v barrel input and a switch on the board, instead of the connector to get the 5v from the original PSU).
I have no original cart but only 2 home made ones, that i use with no issue with both the SF-7000 and its clone. In all my tests, i found that the one or two beeps not always was related to a bad RAM or ROM: cables too long, missing or poor common ground connection and (in my case the more frequent) wrong timing or error in the RAM and ROM CE and OE signals, gave the one or two beeps (somethimes the 3 beeps error too!). I can suggest you to make some test using the ROM that Fabio made for me: https://github.com/fabiodl/sftest |
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Posted: Fri Oct 21, 2022 8:29 am |
I will try to replace the board of my SF as well as make a very tiny board with only 3,5 floppy drive in it. With my homemade I/O cart, with a very short cable, I get 1 beep, but the I checked the EPROM and it's ok. With a cart built by myself I get 2 beep error. What do you think about envelope the cable with the GND? I will try that tool. Thanks. |
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Posted: Fri Oct 21, 2022 11:16 am |
My carts works with cables long 30cm, with no shielding, so i don't think it will resolve your issues.
But it's not clear if your SF-7000 stopped working or never boot up... i started using an 8k game as ROM for testing the ROM enabling / logic was ok.. give a try with Tennis or Guzzler, it worked for me (and was funny use the whole 7000 hw only to run a rom game;) ! |
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Posted: Sat Oct 22, 2022 6:36 am |
I found 4 out of 8 dram chips with a suspicious waveform on the "DOUT" pin. I bet my cable is short enough 😅 |
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Posted: Sat Oct 22, 2022 10:24 am |
Without the floppy, you have no ground in the mainhoard since it's not connected to the case shield Edited: i saw only now you grounded the floppy to the pc with the white wire.. sorry |
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Posted: Sun Oct 23, 2022 8:35 am |
Yes, I remember the post when you wrote that your system won't boot up if drive is disconnected. I checked the PCB for GND connection and the floppy is the only part which close the GND connection, so I built a terminal connector. I found a strange behavior (bottom image) on DOUT signal of 4 of 8 DRAM chips (on top the almost clean signal for - probably - good chips). |
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Posted: Sun Oct 23, 2022 3:50 pm |
I'm not an expert, but in the past i get no DOUT waving signal at all in bad DRAM chips. If you can burn an eprom, try the attached ram test replacing the IPL rom with it. It show if ROM and RAM are OK or KO. |
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Posted: Sun Oct 23, 2022 5:08 pm |
With a metal project box i bought from china and some 3d printed panels, i made a new case for my SF-7017:
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Posted: Mon Oct 24, 2022 11:46 pm |
This is gorgeous! |
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Posted: Wed Oct 26, 2022 1:30 pm |
Awesome! |
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Posted: Wed Oct 26, 2022 4:11 pm |
How do I interpret it? |
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Posted: Wed Oct 26, 2022 4:51 pm |
It seems you get some write error at showed locations. The right screen you should get is the attached (i got it with emulator): |
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Posted: Thu Oct 27, 2022 2:38 am |
I hope I fixed it. The problem was broken LS chips on the I/O cart. I replaced all of them with the 74HCT version. Your test worked as well as you indicated. |
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Posted: Tue Nov 01, 2022 9:52 am |
For anyone's interested, the Kicad projects of both SF-7017 replica board and SC-7326 I/O Cassette cart are published on github:
https://github.com/fabiodl/sf7000 |
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Posted: Fri Nov 18, 2022 10:40 pm |
Thanks to both of you for doing the hard work of publishing this! I will be sure to build one, since Fabio asked me to make sure that my SG-1000 clone had the proper signals on the cart slot to decode the SF-7000's IO ports. (If you want me to send you a bare PCB of the clone please let me know, also! It would be super impressive to have an all-new system from SG to SF, although I still have to build an SK-1100 keyboard clone.) |
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Posted: Sat Nov 19, 2022 9:31 am |
I have a couple of bare pcb left, but internetional shipping from Italy are quite expensive, i suggest you to orderd them directly from china (i spent less than 20€ for five pcbs, + 13€ S.S.). Feel free to PM me if you need more info in ordering. |
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How to make a copy of the SF-7000 floppy disk?
Posted: Wed Feb 14, 2024 10:17 pm
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Hello all,
I hope this is a good topic for this question. If not, I will make a new thread. I recently acquired an SF-7000 for my SC-3000. I want to test it before I go mucking about it (putting in a 34 pin header to use a 3.5" drive, maybe a GoTek, etc etc). The one I got did not come with a DOS disk, unfortunately. I have acquired some blank 3" Amdek disks which *should* work (right?), but I am unsure how to actually make a new DOS disk. Any thoughts? Thanks -M |
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Posted: Thu Feb 15, 2024 9:58 pm |
Hello,
I have a doubt as a result of this thread. Other than some fancy PC with a Mega Drive embedded, is there any other relationship between Sega and IBM? As far as I know, "IPL" is an IBMish term created and (mostly) used by them as of today. As far as I know, this is the only non-IBM system in which the firmware is called this way. Has anybody noticed any other strange term, such as "planar", "ros", etc.? Thank you very much |
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Posted: Thu Feb 15, 2024 10:08 pm |
Sharp and Hudson frequently refer to the initial boot-strapping progress as IPL/initial program loader.
I remember old Motorola documentation referring to it, so I believe it's a quite widespread term, seemingly more common in Japan. |
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Posted: Thu Feb 15, 2024 11:28 pm |
once the SF-7000 is into the cartridge slot, you cannot boot anything other than disks. You have no way to bring in data (tape,etc).
Hence the only way is to make a floppy beforehand. I guess the easiest solution would be to get another 3" floppy (from an amstrad CPC, for instance), make a converter cable and connect it to an old pc motherboard that still has the 34 pin floppy connector. |
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Posted: Fri Feb 16, 2024 1:48 am |
You need a DOS disk.
If you really need it, you can detach the drive from the SF and connect it to a greasewezle interface (you need to buy it). This interface connected to your PC allows you to write any disk images to almost every floppy drive.
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Posted: Fri Feb 16, 2024 3:19 pm |
I never heard of the 'IPL' term until I went on to work with a company that (still) had a mainframe, and mainframe operators (and programmers) in 2002, in Italy. The first time I heard this term I had to ask for its meaning, which I understood was similar to 'bootstrap' in DOS parlance. |
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Posted: Fri Feb 16, 2024 5:11 pm |
[/quote] Thanks. I ordered one and will see what I can do. I had found another procedure, but this one looks a little more straightforward. |
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Posted: Sat Feb 17, 2024 9:42 pm |
Keep attention to the power connector cable.
3 inch drives uses 5V and 12V, but they have a reversed position in the connector unlike the 3,5 inches ones.
Thanks. I ordered one and will see what I can do. I had found another procedure, but this one looks a little more straightforward.[/quote] |
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Posted: Sat Feb 17, 2024 10:23 pm |
[quote="siriokds"]Keep attention to the power connector cable.
3 inch drives uses 5V and 12V, but they have a reversed position in the connector unlike the 3,5 inches ones. [quote="MacRorie"]
Theoretically, couldn’t I leave the power connected via the SF-7000 and just connect the 34pin cable to the greasewezel? -M |
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Posted: Sat Feb 17, 2024 11:34 pm |
No, I wouldn't risk the SF
[quote="MacRorie"][quote="siriokds"]Keep attention to the power connector cable. 3 inch drives uses 5V and 12V, but they have a reversed position in the connector unlike the 3,5 inches ones.
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