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Dock bank

48kB RAM and 16kB ROM in ZX Spectrum is the Home bank. In Timex computers there are two additional independent address area called Dock and EXROM, each has 64kB.

64kB of the address area of Z80 is divided into 8 chunks of 8kB. In each chunkk can be selected Home or Dock/EXROM bank - it is defined by #F4 (244) port. Bit 0 means #0000..#1FFF area, bit 1 - #2000..#3FFF etc. Zeroed bit selects Home bank, set - Dock or EXROM, what depends on bit 7 in #FF (255) port. Dock and EXROM banks cannot be paged in the same time.

Memory map

Section
Addresses
Bit (#F4) =0=1
Chunk Bit 7,(#FF)
=0=1
D
#C000..#FFFF
7
#E000..#FFFF
HOME7DOCK7EXROM7
6
#C000..#DFFF
HOME6DOCK6EXROM6
C
#8000..#BFFF
5
#A000..#BFFF
HOME5DOCK5EXROM5
4
#8000..#9FFF
HOME4DOCK4EXROM4
B
#4000..#7FFF
3
#6000..#7FFF
HOME3DOCK3EXROM3
2
#4000..#5FFF
HOME2DOCK2EXROM2
A
#0000..#3FFF
1
#2000..#3FFF
HOME1DOCK1EXROM1
0
#0000..#1FFF
HOME0DOCK0EXROM0

HOME0 and HOME1 are the ZX Spectrum ROM. Other HOMEx is RAM (HOME2 contains the basic screen).


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Files for download

basicind.txt 18.7kB (2006-06-13 21:21)
Top 32kB of Dock used to run two BASIC programs by unknown author.
docktest.zip 4.8kB (2002-09-29 18:19)
Some ZXVGS software for Dock tests (with sources).

Links to other pages



See also

Timex Computer 2068
Timex Computer 2068.
Timex 2068 : 128kB ROM + 512kB RAM
Internal memory upgrade for Timex Sinclair 2068, Timex Computer 2068 and Unipolbrit Komputer 2086. 128kB ROM, extra 512kB RAM.
BEU - Timex Bus Expansion Unit
Never released expansion for Timex Sinclair 2068 (kind of Plug&Play). Articles by Wes Brzozowski -- analysis how the BEU would work if were finished, from scatterd informations.
Timex Cartridge
Some Timex models provided slot for cartridges.

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© 2009-12-28 21:50 Jarek Adamski, http://8bit.yarek.pl