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  • Joined: 25 Jul 2022
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SF-7000 replica
Post Posted: Mon Aug 15, 2022 11:17 am
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?
sf-7017_1.jpg (129.64 KB)
SF-7000 replica pic 1
sf-7017_1.jpg
sf-7017_2.jpg (144.13 KB)
SF-7000 replica pic 2
sf-7017_2.jpg

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Post 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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Post 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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Post Posted: Mon Aug 15, 2022 10:59 pm
aotta wrote
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?

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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Post 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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Post Posted: Sat Oct 01, 2022 7:10 am
aotta wrote
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


If you need support, ask me.
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Post Posted: Sat Oct 01, 2022 7:50 am
siriokds wrote
aotta wrote
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


If you need support, ask me.


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!
SF7017_3.jpg (426.97 KB)
SF7017_3.jpg
SF7017_6.jpg (286.5 KB)
SF7017_6.jpg

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Post Posted: Yesterday at 4:00 am
aotta wrote
siriokds wrote
aotta wrote
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


If you need support, ask me.


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!


Nice to read it!
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Post Posted: Yesterday at 11:57 am
aotta wrote
siriokds wrote
aotta wrote
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


If you need support, ask me.


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!


Hi, how do you fix the missing floppy issue? For ROM/RAM selection, have you used the 74LS32?
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Post Posted: Yesterday at 12:49 pm
siriokds wrote

...

Hi, how do you fix the missing floppy issue? For ROM/RAM selection, have you used the 74LS32?


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
SF-7017_FD_ok.pdf (383.89 KB)

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Post Posted: Yesterday at 1:54 pm
aotta wrote
siriokds wrote

...

Hi, how do you fix the missing floppy issue? For ROM/RAM selection, have you used the 74LS32?


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



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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Post Posted: Yesterday at 4:47 pm
siriokds wrote

...

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.


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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Post Posted: Yesterday at 7:34 pm
aotta wrote
siriokds wrote

...

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.


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?


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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Post Posted: Yesterday at 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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Post Posted: Today at 5:50 am
aotta wrote
@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


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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