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How does CAS1L, CAS1H, and RAS1 work?


sideburn

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Hi all, 

 

so I just installed a 4MB upgrade into a 520 ST. It’s the new one that Anders Granlund designed (https://github.com/agranlund/STRam) and it’s sort of working. If I disconnect RAS1 then the ST boots with 2MB os ram and everything seems to be working correctly. 
 

But when RAS1 is connected the machine boots to TOS, mounds the hard drive and floppy but the UI is all wonky. The menu bar and menu text is garbled and once you launch an app the machine freezes. 
 

all of my connections look good and the logic board is perfect NOS. 
 

I am leaning towards one of the RAMs being bad but not knowing how RAS and CAS work I really don’t know if both chips are in use or not or maybe there’s some connection failure. 
 

photos attached. 

IMG_6094.jpeg

IMG_6097.jpeg

IMG_6088.jpeg

 

IMG_6085.jpeg

 

IMG_6084.jpeg

IMG_6079.jpeg

Edited by sideburn
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Hello,

 

SDRam can be seen as a grid of memory cells, thus organized primary by Rows (R) and secondary by Columns (C).

 

Thus, basically, to access a given cell, the computer (the MMU in the ST if I do not tell a mistake) first specify the Row on the address lines of the SDRAM, and send a pulse on the... Row Address Strobe (RAS) line. Then the Column is specified and there is a pulse on the Column Address Strobe (CAS) line. There are optimisations, because when a row is "opened" as they say, one can request for a few columns, and thus save some time. There are also limitations, as a SDRam needs to "refresh" all the grid regularly (think of each cell being like a kind of capacitor that lose it's charge overtime).

 

On another topic, to test your RAM, there is a program, YAART if memory serves me right, that could be of use in your case : http://www.chzsoft.de/site/hardware/diverse-kleinigkeiten-fur-den-atari-st/#ram-test-software-yaart

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Thanks yes I already ran YAART and it passed as long as I leave RAS disconnected and the machine only sees 2MB. Once RAS is connected I can only get to the desktop. I cannot run any applications without it crashing. 
 

So what might be going on when I leave RAS disconnected? I was assuming this is causing only one of the two chips to be accessed. No?

 

The two chips are 5118160 Toshiba DRAM

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14 hours ago, sideburn said:

Hi all, 

 

so I just installed a 4MB upgrade into a 520 ST. It’s the new one that Anders Granlund designed (https://github.com/agranlund/STRam) and it’s sort of working. If I disconnect RAS1 then the ST boots with 2MB os ram and everything seems to be working correctly. 
 

But when RAS1 is connected the machine boots to TOS, mounds the hard drive and floppy but the UI is all wonky. The menu bar and menu text is garbled and once you launch an app the machine freezes. 
 

all of my connections look good and the logic board is perfect NOS. 
 

I am leaning towards one of the RAMs being bad but not knowing how RAS and CAS work I really don’t know if both chips are in use or not or maybe there’s some connection failure. 
 

photos attached. 

IMG_6094.jpeg

IMG_6097.jpeg

IMG_6088.jpeg

 

IMG_6085.jpeg

 

IMG_6084.jpeg

IMG_6079.jpeg

 

It occurs to me that there may be a possibility that a wire is shorting to ground. Could you try re-routing the yellow wires through an insulated hole such as a support hole nearby as it looks like a ground short may be possible using the RF suppression holes. Even if there isn't a ground short, I would not recommend routing wires through the RF suppression holes anyway as they are likely to be crushed when fully assembled.

 

 

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2 hours ago, TZJB said:

 

It occurs to me that there may be a possibility that a wire is shorting to ground. Could you try re-routing the yellow wires through an insulated hole such as a support hole nearby as it looks like a ground short may be possible using the RF suppression holes. Even if there isn't a ground short, I would not recommend routing wires through the RF suppression holes anyway as they are likely to be crushed when fully assembled.

 

 

That’s actually an older photo. I rerouted all of them (except A9) to the top of the board. 

Edited by sideburn
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3 hours ago, sideburn said:

So what might be going on when I leave RAS disconnected? I was assuming this is causing only one of the two chips to be accessed. No?

The two chips are 5118160 Toshiba DRAM

 

Yes, if you disconnect the second RAS, only one bank can be accessed. In your case it is one chip per bank.

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1 hour ago, sideburn said:

2nd RAS? I only have RAS1. 

 

I haven't seen the schematics for this expansion, but it needs two RAS signals. And certainly it wouldn't work at all if you would disconnect the only RAS signals available to the expansion board. The other RAS signal, RAS0, is (probably) connencted directly from the soldered pins in place of the older RAM chips.

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