ajp166 at bellatlantic.net
Sat Nov 25 14:49:24 CST 2006
>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.
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