Where to find CAS_INHIBIT SIGNAL in 600XL?

[SS]

I have one of Lotharek's 64 SRAM Modules on order, earmarked for one of my 600XLs.  The instillation instructions seem pretty simple and say to connect one wire to the CAS_INHIBIT SIGNAL, such as Pin 16 of the MMU.  However I am also planning to fit an U1MB board into this machine, which will replace the MMU chip completely.  My question is where else on the 600XL motherboard might I be able to connect to the CAS_INHIBIT SIGNAL *other* than the MMU chip so that I can use both of these boards on the same machine?  Thanks for any advice.

 

...

Edited October 17, 2021 by SS

[Beeblebrox]

3 hours ago, SS said:

I have one of Lotharek's 64 SRAM Modules on order, earmarked for one of my 600XLs.  The instillation instructions seem pretty simple and say to connect one wire to the CAS_INHIBIT SIGNAL, such as Pin 16 of the MMU.  However I am also planning to fit an U1MB board into this machine, which will replace the MMU chip completely.  My question is where else on the 600XL motherboard might I be able to connect to the CAS_INHIBIT SIGNAL *other* than the MMU chip so that I can use both of these boards on the same machine?  Thanks for any advice.

 

...

 

@SS If you don't have any luck regarding finding an alternative CI signal hook up point you could just do one of the old school 64K upgrades, (based around the 2 x replacement 18pin RAM chips and a few jumper wires):

See this thread for the version I did, with a slight variation* to the jumpering of the 8 and 10 pins on U18

 

1. Remove the chip U18 (74S32) from the socket and *link up a jumper wire underneath between pins 8 and 10 on the underside of the board.

2. Remove chips U5 and U6 ( 74LS158 ) . Bend the pins : pin 3 of U5 , U6 to the pin 10. Insert chips back into place so that the bent pins do not come in contact with anything .

3. Connect pin 3 of the A14 U5 and U6 pin 10 of the A15 .

 

Then implement the U1MB upgrade which just requires the usual PHi2, R/W, RST, HLT hook ups and Harting socket cabling in place of the OS and MMU chips.

 

I know this means a redundant 64k SRAM module but I am sure you could sell it on or use it for another 600XL perhaps.

 

Incidentally I had a look around on Google and also AA past topic posts and this may (or may not) help:

To quote"... Thank you Jurgen for confirming what was becoming more and more clear as I did my research. EXTENB is simply an alias for CASinh."

 

Also here:

Quote "

Ok so maybe I've figured it out - I'm assuming that /CI is CASINH, which is the same as EXTENB. From the schematic, it seems that /CI goes into /CE1 for the RAM via a NAND, so that seems to bear that out. In fact I've just noticed the *note saying the same 

 

So I'm assuming that the Ultimate 1MB module from Lotharek will manage /CI so that when the OS wants to access $D8xx -> $DFFF for a parallel bus device, it drives /CI high, thus turning off the RAM (both standard internal 64k and extended 1MB) output and allowing the data-bus to be driven by a parallel bus device that also drives /MPD and /EXT."

 

 

 

Edited October 17, 2021 by Beeblebrox

[flashjazzcat]

My 600XL's VBXE appears to take CASINH from on of the vias connected to pin 38 of the PBI connector.

Edited October 17, 2021 by flashjazzcat

[Beeblebrox]

@SS  or listen to @flashjazzcat 's sage advice   

Edited October 17, 2021 by Beeblebrox

[SS]

@Beeblebrox - Thanks for the advice.  I do actually have a couple of spare 4464 chips lying around that I was going to use for this project but, after some thought, I decided instead on using Lotharek's board so that this upgrade could be totally reversible later if wanted.  The thread links that you provided really helped though because they told me that I was looking for EXTENB, which was another name for CAS_INHIBIT.  Then when Jon said that I could run my wire to the PBI connector, I knew exactly what I was looking for.  

https://www.atarimax.com/jindroush.atari.org/atpbi.html

 

@flashjazzcat - This is probably going to be a dumb question but can I simply run a wire around to the bottom of the motherboard and solder it directly to PBI pin 38?  Thanks.

[Beeblebrox]

18 minutes ago, SS said:

@Beeblebrox - Thanks for the advice.  I do actually have a couple of spare 4464 chips lying around that I was going to use for this project but, after some thought, I decided instead on using Lotharek's board so that this upgrade could be totally reversible later if wanted.  The thread links that you provided really helped though because they told me that I was looking for EXTENB, which was another name for CAS_INHIBIT.  Then when Jon said that I could run my wire to the PBI connector, I knew exactly what I was looking for.  

https://www.atarimax.com/jindroush.atari.org/atpbi.html

 

@flashjazzcat - This is probably going to be a dumb question but can I simply run a wire around to the bottom of the motherboard and solder it directly to PBI pin 38?  Thanks.

@SS  No worries. No a dumb question at all. I'd probably go with FJC's suggestion to hook it off 38 on the PBI. You could connect to it directly but just as easy to find a connection running off it nearby which then means it doesn't interfere with the PBI connector. Using your multimeter continutity check to confirm, just find the trace that leads off 38 to a solder point nearby and hook up to that. 

 

So just looking at some images of one of my 600XL's board, 38 is on the underside:

 

 

.... so it should be here on the top side you can hook up to:

 

 

Just double check it visually and for continuity. Your 600XL's board should be the same as mine.

Edited October 17, 2021 by Beeblebrox

[SS]

@Beeblebrox - Fantastic! Thank you for all of your help. ?

[BillC]

On 10/17/2021 at 7:14 AM, SS said:

I have one of Lotharek's 64 SRAM Modules on order, earmarked for one of my 600XLs.  The instillation instructions seem pretty simple and say to connect one wire to the CAS_INHIBIT SIGNAL, such as Pin 16 of the MMU.  However I am also planning to fit an U1MB board into this machine, which will replace the MMU chip completely.  My question is where else on the 600XL motherboard might I be able to connect to the CAS_INHIBIT SIGNAL *other* than the MMU chip so that I can use both of these boards on the same machine?  Thanks for any advice.

 

...

The CAS_INHIBIT signal is an output on pin 16 of the MMU, while the Sobola 600XL schematics don't show it, it connects to the EXTEN signal and pin 9 of U7. I found this on page 67 of the schematics in the 600XL Field Service Manual.

http://www.atarimania.com/documents/Atari_600XL_Computer_Field_Service_Manual_Rev_1.pdf

[+scorpio_ny]

On 10/17/2021 at 5:35 PM, SS said:

@Beeblebrox - Thanks for the advice.  I do actually have a couple of spare 4464 chips lying around that I was going to use for this project but, after some thought, I decided instead on using Lotharek's board so that this upgrade could be totally reversible later if wanted.  The thread links that you provided really helped though because they told me that I was looking for EXTENB, which was another name for CAS_INHIBIT.  Then when Jon said that I could run my wire to the PBI connector, I knew exactly what I was looking for.  

https://www.atarimax.com/jindroush.atari.org/atpbi.html

 

@flashjazzcat - This is probably going to be a dumb question but can I simply run a wire around to the bottom of the motherboard and solder it directly to PBI pin 38?  Thanks.

One can actually do the upgrade with the 4464 chips that is reversible. One of the wiring variations, you solder wires on to the chips only. No soldering on the motherboard.

 

Edited October 19, 2021 by scorpio_ny
Added missing word

[SS]

19 hours ago, BillC said:

The CAS_INHIBIT signal is an output on pin 16 of the MMU, while the Sobola 600XL schematics don't show it, it connects to the EXTEN signal and pin 9 of U7. I found this on page 67 of the schematics in the 600XL Field Service Manual.

http://www.atarimania.com/documents/Atari_600XL_Computer_Field_Service_Manual_Rev_1.pdf

Thanks @BillC. 

This would certainly be a shorter path to take.  Would I solder the wire directly to the socketed pin or would I need to bend the pin up first?  I do have a partially scavenged board lying around with an extra one of those chips still on it so I would still have a spare in reserve just in case. 

 

...

Edited October 19, 2021 by SS

[flashjazzcat]

Wires soldered to chip legs can be a king sized pain in the ass on socketed motherboards. I always groan when I encounter one.

 

 

[BillC]

11 hours ago, SS said:

Thanks @BillC. 

This would certainly be a shorter path to take.  Would I solder the wire directly to the socketed pin or would I need to bend the pin up first?  I do have a partially scavenged board lying around with an extra one of those chips still on it so I would still have a spare in reserve just in case. 

 

...

I agree with FJC, I don't like wires soldered to the chips if it can be avoided and this would also require extra work when the MMU is removed to install a U1MB upgrade. While the wire path is longer the I prefer to use vias as suggested in post# 6 if available, it might be possible to follow the trace and locate a closer via as well.

[+scorpio_ny]

HI @SS,

 

You had mentioned that you had a couple of extra 64 chips that you were going to use initially for this project. I had done the upgrade using the two chips and it only required installing three wires and lifting a pin or two ( sorry @flashjazzcat and @BillC ). It was a very easy upgrade. I had posted pictures and a link to the instructions that I followed on this thread: 600XL Composite and Audio upgrade 

 

Maybe @flashjazzcat and @BillC can weigh in following this memory upgrade path in relation to installing the U1MB upgrade with it if it would be easier?

 

[SS]

@scorpio_ny - Not to worry, those 4464 chips are not going to go to waste.  I still have two other 600XLs waiting in the wings for some other modifications.  The next one after this project will get a UAV and probably a 32-in-1 board as well as the 64K upgrade.  I very much like upgrading different machines in different ways.

[+scorpio_ny]

56 minutes ago, SS said:

@scorpio_ny - Not to worry, those 4464 chips are not going to go to waste.  I still have two other 600XLs waiting in the wings for some other modifications.  The next one after this project will get a UAV and probably a 32-in-1 board as well as the 64K upgrade.  I very much like upgrading different machines in different ways.

Oh nice! Looks like you are going to be busy with some nice projects.

[Beeblebrox]

4 hours ago, scorpio_ny said:

HI @SS,

 

You had mentioned that you had a couple of extra 64 chips that you were going to use initially for this project. I had done the upgrade using the two chips and it only required installing three wires and lifting a pin or two ( sorry @flashjazzcat and @BillC ). It was a very easy upgrade. I had posted pictures and a link to the instructions that I followed on this thread: 600XL Composite and Audio upgrade 

 

Maybe @flashjazzcat and @BillC can weigh in following this memory upgrade path in relation to installing the U1MB upgrade with it if it would be easier?

 

@scorpio_ny my 600XL 64k mod method worked well the other month as detailed here:

 

 

 

[SS]

Thanks again @Beeblebrox.  Those pictures of the U1MB connections in particular will help a lot.  ??

[Beeblebrox]

8 minutes ago, SS said:

Thanks again @Beeblebrox.  Those pictures of the U1MB connections in particular will help a lot.  ??

@SS no worries. Just to say with regards to the u1mb side of things just read the other forum member replies to that thread. I cite FJC's video in it and that is fine to follow. 

[Sinjinhawke]

On 10/19/2021 at 3:37 PM, flashjazzcat said:

Wires soldered to chip legs can be a king sized pain in the ass on socketed motherboards. I always groan when I encounter one.

 

 

I did recently solder wires to chip legs while upgrading a 600xl to 64kb.   I feel much shame.   Maybe I should have popped it into a 2nd socket and bent the legs on the socket instead.  I may in fact try to go back and remedy it when I get some spare hours.

[SS]

55 minutes ago, Sinjinhawke said:

Maybe I should have popped it into a 2nd socket and bent the legs on the socket instead. 

This is a good idea.  I should remember to do this.

[Beeblebrox]

1 hour ago, SS said:

This is a good idea.  I should remember to do this.

@SS Does sound like a good idea. Incidentally I definitely found the original 74 logic chips on my 600XLs had brittle legs which don't like being bent after decades in situ. I ended up replacing them with new ones after legs snapped off right near the IC body with at least one whilst doing the upgrade. Thankfully they are dirt cheap.

 

The main tip passed into me by tf_hh when doing the variation of the 64K mod I linked to above is not to bridge pins 8-10 of U18 (74S32) by simply pushing a wire into the socket wipes top side, but to use a soldered jumper wire on the underside of the PCB to jump them. (A wire just pushed into the socket can come loose over time and also potentially short out the board in the process if it falls out.)

[+kheller2]

1 hour ago, Beeblebrox said:

@SS Does sound like a good idea. Incidentally I definitely found the original 74 logic chips on my 600XLs had brittle legs which don't like being bent after decades in situ. I ended up replacing them with new ones after legs snapped off right near the IC body with at least one whilst doing the upgrade. Thankfully they are dirt cheap.

 

The main tip passed into me by tf_hh when doing the variation of the 64K mod I linked to above is not to bridge pins 8-10 of U18 (74S32) by simply pushing a wire into the socket wipes top side, but to use a soldered jumper wire on the underside of the PCB to jump them. (A wire just pushed into the socket can come loose over time and also potentially short out the board in the process if it falls out.)

That's why you remove the socket too and just jumper the holes

 

[Beeblebrox]

6 hours ago, kheller2 said:

That's why you remove the socket too and just jumper the holes

 

@kheller2 sure, you can do that. The version I did just negates the extra step/need to remove the socket (should you want to reverse the mod or avoid the possibility of damage to the pcb in removing it). It was more of a forewarning against the version I've seen where a bridging wire pushed into the socket is used. ?

[joeatari]

Did you finish this project and also hook up EXT_SEL once you received the 64 SRAM module?  I'm in the middle of the exact same project, and would like to also find the EXT_SEL location for 600XL.