MEGA ST internal Floppy

[Shift838]

I am wondering if I can have 2 floppy drives hooked up to the internal floppy controller connector.  One to be the standard ST floppy for A: and for B: a gotek (micro gotek).  

 

Or will that connector only respond to one drive connected.  I cannot recall if that is the case and I have to use the external drive connector on the back of the Mega ST.

 

 

[TGB1718]

Looking at the wiring diagram, it looks like only floppy A is connected to the internal connector, if you wanted

to do this, you would have to solder in a jumper from the floppy B select line to the internal connector.

 

Then just by setting one floppy to 0 and the other to 1 it should work.

 

I had external floppy drives for my STM bitd, one of which was a 5 1/4 double sided drive, so I included a switch

so that I could boot from either floppy, not sure if you would want this too, in which case it's bit more involved.

[Shift838]

15 hours ago, TGB1718 said:

Looking at the wiring diagram, it looks like only floppy A is connected to the internal connector, if you wanted

to do this, you would have to solder in a jumper from the floppy B select line to the internal connector.

 

Then just by setting one floppy to 0 and the other to 1 it should work.

 

I had external floppy drives for my STM bitd, one of which was a 5 1/4 double sided drive, so I included a switch

so that I could boot from either floppy, not sure if you would want this too, in which case it's bit more involved.

Are you saying that drive select 1 (0 for A; 1 for B) is not connected at all and even using a dual floppy cable would not work?  If I run a jumper wire from pin 12 on Drive B to pin #10 of the floppy connector then set the second drive to drive B, it should work?

 

Do you have a link to the wiring diagram you are referring to.

 

Thanks,

 

 

 

[TGB1718]

7 hours ago, Shift838 said:

Do you have a link to the wiring diagram you are referring to.

In these manuals

MEGA ST 4.pdf Mega_ST2-4_Schematic_2-19-1987.pdf

[Shift838]

7 hours ago, TGB1718 said:

In these manuals

MEGA ST 4.pdf 5.24 MB · 1 download Mega_ST2-4_Schematic_2-19-1987.pdf 1.69 MB · 1 download

If you are stating just a jumper wire from floppy 1 drive select (drive b - pin #12) over to floppy 0 drive select line pin #10 that does not work even with one drive configured as DS0 and the other as DS1, neither respond.

Edited April 3, 2023 by Shift838

[351cougar]

test to see if message goes thru. member  since 2015 but see message needs mod approval. 

[Albert]

36 minutes ago, 351cougar said:

test to see if message goes thru. member  since 2015 but see message needs mod approval. 

Only your first few posts.

 

 ..Al

[351cougar]

notice ds0 hard wired to J12-10 ds1 is jumpered default (w1 2-3) going to J13 -5 which is while not shown ds0 select on drive. J13 -6 which is ds1 is default jumpered thru w1 2-3, to be pulled up. This was due to initial systems had no internal drive so both ds's needed to get out of the case. They left in some selections on that with the w1 and w5 jumpers for this machine. For what you want , remove jumper from w1 completely. jumper wire from w1-3 or w5 -1 to J12-12 which I believe is ribbon cable ds1. you have to remember to not use external connection in that state. Also I believe all Atari drives default to ds0, so config drives on internal ribbon accordingly. 

[Shift838]

On 4/10/2023 at 7:27 PM, 351cougar said:

notice ds0 hard wired to J12-10 ds1 is jumpered default (w1 2-3) going to J13 -5 which is while not shown ds0 select on drive. J13 -6 which is ds1 is default jumpered thru w1 2-3, to be pulled up. This was due to initial systems had no internal drive so both ds's needed to get out of the case. They left in some selections on that with the w1 and w5 jumpers for this machine. For what you want , remove jumper from w1 completely. jumper wire from w1-3 or w5 -1 to J12-12 which I believe is ribbon cable ds1. you have to remember to not use external connection in that state. Also I believe all Atari drives default to ds0, so config drives on internal ribbon accordingly. 

 

I have found locations W1 and W5, there is no jumper on the board for these locations, so it does not seem it was jumpered in any way from the factory.  (see attached photo).

 

So to clarify do I need to run a wire from W1-3 and W5-1 to pin #12 on J12 or do i just need to pick W1 or W5 and only do one of them?

 

Edited April 13, 2023 by Shift838

[351cougar]

I have looked at some hi rez MB scans online and dont see jumpers on those pins on any of them. Schematic , if its correct, means they have to be connected for external FD to work. What I guess they did , on most boards, is a solder blob short on the underside of the pcb. saving a few cents on headers and jumpers almost no one would use. You will have to DMM buzz out the connections to the points shown on the schematic to verify. Then undo the solder blob  that would represent the jumper I stated above. Only one of the points I state is needed as W1-3 and W5-1 are the same (ds1sel)

[Shift838]

11 hours ago, 351cougar said:

I have looked at some hi rez MB scans online and dont see jumpers on those pins on any of them. Schematic , if its correct, means they have to be connected for external FD to work. What I guess they did , on most boards, is a solder blob short on the underside of the pcb. saving a few cents on headers and jumpers almost no one would use. You will have to DMM buzz out the connections to the points shown on the schematic to verify. Then undo the solder blob  that would represent the jumper I stated above. Only one of the points I state is needed as W1-3 and W5-1 are the same (ds1sel)

I did check on the back side of the board to see if there was a bridged connection to act as a jumper or jumper wire, there looks to be an actual trace between pins 2 and 3 on both W1 and W5.

 

I have verified continuity with those pins.

 

continuity on W5 - pins 2 and 3

Continuity on W1 - pins 2 and 3 on W1 and on W5 Pini 1

I believe I would need to cut the trace between pins 2 and 3 on each of the W1 and W5, correct?  then connect one of the points you stated.  Correct?

 

 

Edited April 14, 2023 by Shift838

[351cougar]

cut W1 2-3 and leave W5 2-3 alone. That pulls up DS 1 thru R111, so it cant be selected if an external drive is plugged in. you can jumper w1-2 to W5 2-3 if you want, to also pullup DS0 line at external FD connection. then wire W5-1 or W1-3 to J12-12 . Before doing any jumpers buzz the connections after cutting to verify they are actually disconnected. don't want any potential bus shorts.  

[Shift838]

On 4/14/2023 at 9:26 PM, 351cougar said:

cut W1 2-3 and leave W5 2-3 alone. That pulls up DS 1 thru R111, so it cant be selected if an external drive is plugged in. you can jumper w1-2 to W5 2-3 if you want, to also pullup DS0 line at external FD connection. then wire W5-1 or W1-3 to J12-12 . Before doing any jumpers buzz the connections after cutting to verify they are actually disconnected. don't want any potential bus shorts.  

So i did this and it works.  I am wondering though if I want the physical floppy to be drive B and the Gotek to be Drive A, if I need go to J12-10 instead of J12-12?  also do not see any jumpers to reconfigure the physical drive as B: drive.  Could I use a twisted floppy cable to accomplish this?

 

Thanks!

Edited April 18, 2023 by Shift838

[351cougar]

gotek probably has the ds select avail, but if internal doesn't, you'll have to use a PC cable swap (twist) . J12-10 is hardwired to ym2149 so you'd have to cut the trace. There is no jumper to make the selection.

[Shift838]

2 hours ago, 351cougar said:

gotek probably has the ds select avail, but if internal doesn't, you'll have to use a PC cable swap (twist) . J12-10 is hardwired to ym2149 so you'd have to cut the trace. There is no jumper to make the selection.

instead of cutting the trace i could socket the YM2149 IC since i have some 40 pin DIP socket.  Then just bend out pin #20 on the socket (from what I see on the schematic).

 

 

[Shift838]

On 4/18/2023 at 8:25 PM, 351cougar said:

gotek probably has the ds select avail, but if internal doesn't, you'll have to use a PC cable swap (twist) . J12-10 is hardwired to ym2149 so you'd have to cut the trace. There is no jumper to make the selection.

desolder the YM2149 and put a socket in place, plugged it in and left pin #20 out of the socket, used a PC floppy cable with a twist, took the jumper off of the gotek so to use only the cable for the drive select.  Neither drive will work, just get a error that states the drive does not exist.

 

 

[TGB1718]

I think this is because the ST only has one Motor On signal that goes to both drives at the same time,

the twisted cable swaps drive A: B: and Motor On A: and B: so I don't think you have a Motor on signal

going to either drive.

 

The twisted cable is really only a PC thing, When I had 4 floppy's connected to my ST (only 2 active at the same time)

I just used a normal flat 34 way cable, no twist.

 

 

[351cougar]

according to this site http://www.interfacebus.com/PC_Floppy_Drive_PinOut.html pins 10 - 16 are swapped on that cable. But what I dont understand is 10 and 16 are motor enables and 12 and 14 are DS BUT the ST doesnt have 12 or 14 connected on the ribbon. Atari used the 2149 for only the side select and drive select signals everything else comes from the 7406 chip. Maybe there was a current drive or timing limitation, there had to be some reason for not having everything come from a single chip. 

 Having pin 20 lifted on the 2149 means there is no D0sel (drive A) only d1sel (drive B) . you said before both drives worked, you just wanted for A to be B and vice versa, or at least the ability for that.  If that is the case and as TGB says just use a straight cable, and wire up a DPDT switch to swap DS's and mount to outside of case.