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Myarc HFDC Mod


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#1 BeeryMiller ONLINE  

BeeryMiller

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Posted Thu Dec 7, 2017 11:02 AM

Quick question, I purchased a HFDC from Roman and got it in this week.  There is a modification on it I have not seen unless it was a repair.

 

There are some wires running from some chips (I am at work so I do not recall the chips) to a dip switch.  Was there a modification that changed whether a hard drive would be searched first?

 

Beery



#2 InsaneMultitasker OFFLINE  

InsaneMultitasker

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Posted Thu Dec 7, 2017 10:18 PM

It might be the 2-wire modification to bypass the signal from the MFM drive to the controller that results in a 15-20 second timeout during each powerup.  It is usually employed when the HFDC is used as a floppy controller with no hard drives attached, so that you don't have to wait for the controller/hard drive to time out. 



#3 mizapf OFFLINE  

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Posted Fri Dec 8, 2017 4:43 AM

Isn't that also done by a CRU bit that was mentioned in the 4th edition of the HFDC manual?

 

ftp://ftp.whtech.com/datasheets%20and%20manuals/Hardware/Myarc/MYARC%20HFDC%20Manual%204th%20edition.pdf

 

(page 46)



#4 atrax27407 OFFLINE  

atrax27407

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Posted Fri Dec 8, 2017 5:33 AM

I have a couple of EPROMs that will take care of that problem in the DSR without wires. One removes floppy drive access and a second that removes hard drive access



#5 Schmitzi OFFLINE  

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Posted Fri Dec 8, 2017 4:22 PM

:music: :lust:



#6 InsaneMultitasker OFFLINE  

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Posted Fri Dec 8, 2017 10:52 PM

Isn't that also done by a CRU bit that was mentioned in the 4th edition of the HFDC manual?

 

ftp://ftp.whtech.com/datasheets%20and%20manuals/Hardware/Myarc/MYARC%20HFDC%20Manual%204th%20edition.pdf

 

(page 46)

Probably one and the same - the documented CRU bit is what is being tied low to trick the DSR into thinking the hard drive is ready.  If the hard drive is not physicall ready (disconnected or not spun up) it cannot be read, the DSR cannot load sector 0, and the HFDC thinks the hard drive is uninitialized. 

 

Thus if no hard drive is ever connected, the error condition is returned for each access; however, if a hard drive IS connected, the DSR will force a sector 0 read the next time the DSR tries to access that drive.






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