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Old 18 August 2018, 00:10   #1
jagLally
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scsi2sd adaptor v5 to GVP Impact externally

Hi,

I managed to get scsi2sd adaptor V5 working with GVP Impact Series II A500 HD8 with Amiga 500, Workbench 1.3. http://amigakit.amiga.store/product_...oducts_id=1264

However, I fiddle and experiment and need to remove the SD card quite a bit, but I don't want to have to remove the GVP drive cover or leave it off permanently.

So, I was thinking to buying this 25-PIN FEMALE DSUB DB25 TO 50-WAY IDC FEMALE SCSI ADAPTER http://amigakit.amiga.store/product_...oducts_id=1290 and have the scsi2sd adaptor outside on the back.

For power I was thinking of using the mini usb connector or try to route the molex plug outside.

Will this work and the GVP board couldn't care less if the SCSI device is connected internally or externally (as far as it's concerned it's just on the SCSI bus)?

Are there any gotchas or something logically different from the GVP board/Amiga 500 point of view if I have a device on the outside port instead of the internal one?

Has anyone done this and made it work?

Any opinions or educated guesses?
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Old 18 August 2018, 02:47   #2
idrougge
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A SCSI controller only cares about termination, not about whether a device is external or internal.
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Old 18 August 2018, 03:38   #3
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You can get a Micro Sd extension cable. The cable is flat enough to be routed outside of the GVP case without issue.

https://www.amazon.com/Gplink-Extens...on+cable&psc=1
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Old 18 August 2018, 12:05   #4
jagLally
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Quote:
Originally Posted by Sinphaltimus View Post
You can get a Micro Sd extension cable. The cable is flat enough to be routed outside of the GVP case without issue.

https://www.amazon.com/Gplink-Extens...on+cable&psc=1
I hadn't thought of that. I will look into it. My only immediate concern is that I might get issues with micro movement of connection pins. I've read posts of people using micro SD to SD adaptors in cameras and having issue with micro movement and cards stop working.

Quote:
Originally Posted by idrougge View Post
A SCSI controller only cares about termination, not about whether a device is external or internal.
Ah good to know that it doesn't matter. The scsi2sd card will get id 0 regardless of it's physical connection.

Thank you both of you.
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Old 18 August 2018, 14:32   #5
patrik
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@JagLally:

The A500 GVP controllers are usually not terminated internally, just relying on the termination to be present on the harddrive in combination with the short cable ~10cm cable. Stubs of ~10cm are allowed on a scsi chain according to spec and this creates a scsi chain of 0cm at the harddrive where the termination is and the controller will be on the stub.

If you have an external device with some sort of cable length, you will need internal termination as the total scsi chain length becomes long enough to create reflections, which is the reason you have termination.

This raises another issue with the GVP cards which are that they do not provide termination power to the bus (you should measure just below 5V at pin 26 on the internal connector and pin 25 on the external connector). With harddrives, you can usually bodge-fix this by setting the drive to either power its own termination or supply termination power to the bus, but say if you have a separate terminator internally, it will need termination power supplied from the bus, disregarding if it is an passive or active terminator.

Measure to verify termination power and check if the SCSI2SD can be configured to supply termination power to the bus, then measure again - without termination power separate terminators cannot work.
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Old 18 August 2018, 19:34   #6
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I think most GVP controllers do have soldered-on termination resistor packs. For proper operation with both internal and external devices, those should be removed and an external terminator used.

In practice things might work OK without removing the on-board termination, even with one or two external devices however.

If you look at the Impact A500 HD8+ Series II page on amiga.resource.cx, the rev.3 board pic shows three resistor packs next to the SCSI chip. The rev.6 board pic shows only one resistor pack with empty spaces where another two would be. (I guess it's possible that the owner of that board removed them?)
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Old 19 August 2018, 02:16   #7
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My A500 GVP had socketed terminators. I had to remove them (just pull them out) only to use internal and external and provide my own termination at the end of each chain.
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Old 19 August 2018, 19:00   #8
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This is turning out to be more complicated than I thought.

I understand the logic for termination but will have to get my head around what provides the power etc.

I was hoping for a very small scsi db25 male to male cable to connect GVP to SCSI2SD using the adaptor. Searching around, it seems the db25 male to male cables are designed for 1m or more length and they are not cheap. I really only want around 5cm or less.

I looked into just standard db25 male/male connectors typically used to join two cables, but that wouldn’t allow the GVP drive + 25 to 50 adaptor + SCSI2SD to sit flat on the table as the port on GVP is at the bottom.

Looks like MicroSD to SD cable routed to outside might be my best and cheapest option. Expensive db25 male to male and uncertainty on terminators are my two deal breakers.
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Old 19 August 2018, 19:04   #9
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For what it' worth, I use that extension on 3 different devices (my Vampire card and two different rPis) without any issues. you'll just need a micro sd to full size sd adaptor also. I haven't found an extension that goes from micro to micro, only a micro to standard size. but as you know, just about every micro sd card you buy comes with one.

Last edited by Sinphaltimus; 19 August 2018 at 19:05. Reason: fixed typo
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Old 19 August 2018, 19:31   #10
jagLally
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Quote:
Originally Posted by Sinphaltimus View Post
For what it' worth, I use that extension on 3 different devices (my Vampire card and two different rPis) without any issues. you'll just need a micro sd to full size sd adaptor also. I haven't found an extension that goes from micro to micro, only a micro to standard size. but as you know, just about every micro sd card you buy comes with one.
Any reason why you wouldn’t use a full size sd card rather than an adaptor to micro sd again? Is there anything I’m missing here like it won’t work as the original slot is micro?
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Old 21 August 2018, 02:32   #11
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Quote:
Originally Posted by jagLally View Post
Any reason why you wouldn’t use a full size sd card rather than an adaptor to micro sd again? Is there anything I’m missing here like it won’t work as the original slot is micro?
No, No reason really. I just buy micro-sd cards as a preference. I don't know if there are technical differences in performance or not. Just that everything uses them these days.
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