z8000 segment scheme question

From: Joe R. <rigdonj_at_cfl.rr.com>
Date: Thu Aug 5 13:15:13 2004

  If anyone is serious about building a Z8000 machine, I'll donate a CPU
card complete with 7Mb memory, Z-8001 CPU, MMUs, DTC, CIC, SCC, etc. See


At 05:19 PM 7/26/04 -0700, you wrote:
> If you guys are intending to build a Z8000 machine to
>run CP/M-8000, you should let me know. There are a couple
>hardware restrictions you should know about early on.
>>From: "Kane, David (DPS)" <David.Kane_at_aph.gov.au>
>>The Z8000 segmented address scheme has two forms. The long form that you
>>described uses two 16 bit values (registers or memory locations). The
>>short form uses a single 16 bit value with the 7 bit segment number in
>>bits 9-15 and an 8 bit offset into the segment in bits 1-8. Bit 16 of
>>the first 16 bit value is a flag which indicates long or short segment
>>address. This is important for memory addresses operands as the CPU can
>>get an address word operand from memory, and then based on the flag bit
>>can decide if the next word must be read to get the complete long
>>address. In either case the segment address is located in the same place
>>in either a short segment address or the first word of a long segmented
>>> -----Original Message-----
>>> From: cctalk-bounces_at_classiccmp.org
>>> [mailto:cctalk-bounces_at_classiccmp.org] On Behalf Of SHAUN RIPLEY
>>> Sent: Monday, 26 July 2004 1:27 PM
>>> To: cctalk_at_classiccmp.org
>>> Subject: z8000 segment scheme question
>>> I picked up one of my computer books today and read
>>> that z8000 uses one 16 bit register to hold the 7 bit
>>> segment number and one register to hold the 16 bit
>>> offset. The strange thing is that the segment number
>>> is hold in position of bit 9-14 other than the bottom
>>> half of the first register. I goggled and found
>>> complaint about this scheme but no one explained why
>>> it was designed so. Could somebody on the list tell me why?
>>> __________________________________
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Received on Thu Aug 05 2004 - 13:15:13 BST

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