Northstar Horizon

Allison ajp166 at
Sat Nov 25 14:49:24 CST 2006

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


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