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5150 Memory Errors


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#1 eebuckeye OFFLINE  

eebuckeye

    Stargunner

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Posted Sat Jan 19, 2019 11:53 PM

I picked up a 5150 and have spent my night trying to figure out memory configurations.
 
When I first got the 5150 it had the AST SixPack Plus adapter installed with 1 bank and the computer reported 128k memory.
 
I removed the AST SixPack Plus and got a 1001 201 error when booting which I thought was odd.  I checked SW1 on the motherboard and got the following:
 
- 3 on, 4 off 1001 201 49152 bytes
- 3 off, 4 off 1001 201 will not boot
 
It is a PC1 motherboard and all memory banks are full.  With the AST SixPack Plus adapter installed I got 128k.  The SixPack Plus was set to start at 64k (dip switches 1,2,3 are off)
 
I then tried the following AST dip switch configurations per the users manual:
 
- AST 4,5 off 6 on – bank 1 only active (bank 1 and 2 populated), no boot error, 131,072 bytes free
- AST 4,6 off, 5 on – bank 1-2 active with 2 banks memory, no boot error 131,072 bytes 
- AST 4,6 off, 5 on – bank 1-2 active with 2 banks memory, no boot error 131,072 bytes (same as previous but swapped with different memory)
- AST 4, off, 5-6 on – bank 1-3 active with 3 banks memory, no boot error 131,072
 
I do not understand why I do not report at any time greater than 128k of memory.  I do not receive boot errors when the AST is installed either.
 
I am using DOS 1.1 chkdsk to see the available memory.
 
I do not understand why I get memory errors when I remove the AST adapter.  I also do not understand why the memory does not increase when I add banks of memory and change the dip switches on the AST adapter.  Again no memory errors.
 
Any suggestions please?
 
Thank you!


#2 ChildOfCv OFFLINE  

ChildOfCv

    Moonsweeper

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Posted Sun Jan 20, 2019 3:58 AM

I was a little confused by your description of which banks are populated, but based on what I think you said, the following applies.

In spite of what the manual says, DIP SW 1 pins 3,4 specify how many 16K's are on the main board.  Have them both off for the first 64K.
 
 

When I first got the 5150 it had the AST SixPack Plus adapter installed with 1 bank and the computer reported 128k memory.

...

It is a PC1 motherboard and all memory banks are full.


To be clear, are you saying that the PC has all banks full, but the AST has only 1 bank? That sounds like a minimum of 256K + whatever size of memory is on the AST. Each bank on the main board gives it 64K.

With the AST SixPack Plus adapter installed I got 128k.


How are SW2's switches set? While SW1 tells the BIOS how much "base RAM" you have, SW2 is the total RAM.

The SixPack Plus was set to start at 64k (dip switches 1,2,3 are off)

If all the banks on the main board are full, you should be starting at 256K (S1 off, S2 on, S3 on).


I then tried the following AST dip switch configurations per the users manual:
 
- AST 4,5 off 6 on – bank 1 only active (bank 1 and 2 populated), no boot error, 131,072 bytes free
- AST 4,6 off, 5 on – bank 1-2 active with 2 banks memory, no boot error 131,072 bytes 
- AST 4,6 off, 5 on – bank 1-2 active with 2 banks memory, no boot error 131,072 bytes (same as previous but swapped with different memory)
- AST 4, off, 5-6 on – bank 1-3 active with 3 banks memory, no boot error 131,072

SW2 is almost certainly set for a total of 128K. So that is all that the BIOS is ever going to look for, and what it's going to report as the memory size.

#3 ChildOfCv OFFLINE  

ChildOfCv

    Moonsweeper

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Posted Sun Jan 20, 2019 4:30 AM

And looking over the BIOS listings, it's as you might guess:  If SW1 specifies less than 64K, then BIOS completely ignores the contents of SW2.  Otherwise it adds the value of SW2 (1-5) in 32K increments to the 64K that is already specified by SW1 pins 3,4.  So most likely what you have for getting 128K total is SW1 = off, off  SW2 = off, off, off, on, off.  For 256K, SW2 should be off, off, on, on, off.


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#4 eebuckeye OFFLINE  

eebuckeye

    Stargunner

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Posted Mon Jan 21, 2019 12:46 AM

Thanks for all the information! I got everything to work now!






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