Northstar Horizon - test-drb@ccmp.vtda.org

25 Nov 2006

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Subject: Re: Northstar Horizon
   From: "Dave Dunfield" <dave06a at dunfield.com>
   Date: Sat, 25 Nov 2006 13:29:16 -0500
     To: "General Discussion: On-Topic and Off-Topic Posts"	<cctalk at
classiccmp.org>

  On 25 Nov 2006 at 3:27, jim stephens wrote:

  And my memory of 256 bytes may be off, I vaguly
recall maybe on 32 bytes 
 are visible and used by the processor at boot.  People had to use pretty small proms 
 in the early days of the hobby.  
 I recall that the disk controller had a small bipolar prom and that 
 it was indeed 32 bytes.  It was miles better than toggling the boot 
 code by hand...  A 256-byte boot prom back then would have been an 
 almost obscene luxury... ;) 
Well - then I guess NorthStar was obscene... :-)

The single-density controller does indeed have 256 byte of ROM (in three chips!)
The double-density one has 512 bytes of ROM. 
the boot rom was two 256x 4 parts (bipolar) and the third was the address
decode for the board (also 256x4 bipolar).

...

The controller occupies 1K of memory space from E800-EBFF
   E800-EFFF  ROM on DD,  unused or mirror ROM on SD
   E900-E9FF  ROM on both SD and DD
   EA00-EAFF Hardware control (address is write value)
   EB00-EBFF Write data (address is data)

I might have EA00 & EB00 reversed, it's been a while since I was in the
nuts and bolts of the N* controller. 
Without checking the manuals thats about right.

Allison