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.

ZXVGS UPB upgrade

Was designed in 2001 year. Allowed two operation modes: 2068 and ZXVGS, selected by manual switch. 32kB SRAM was seen only in EXROM bank: in 2068 mode in top half, in ZXVGS mode in bottom. For the EPROM there were seveal options depending on its size - 32kB, 64kB, 128kB.

Was made as ZXVGS mode only, using 64kB ROM (two ZX128 banks, ZXVGS code in ROM0, second half used for TR-DOS traps) and 32kB SRAM.

128kB PEROM and 512kB SRAM

In year 2005 the prices of PEROM (Flash EPROM) and SRAM got lower, so most advanced upgrade can be made.

The best solution for the PEROM switching is probably the FlashD0 board, upgraded in v004 version with EXROM option and write protection.

Switching of the SRAM should keep compatibility with ZXVGS UPB and extension called Larken ramdisk.

Memory map

Chunk	Addresses	Home	Dock								EXROM
7	#E000..#FFFF	RAM	0	1	2	3	4	5	6	7	ROM
6	#C000..#DFFF
5	#A000..#BFFF
4	#8000..#9FFF
3	#6000..#7FFF
2	#4000..#5FFF
1	#2000..#3FFF	ROM (BASIC)
0	#0000..#1FFF	ROM (BASIC)

Each chunk can point to Home or Dock/EXROM.
Dock and EXROM are exclusive. Only one of them can be selected at a time.
Screen is located in Home, chunks 2 and 3.

The 512kB SRAM is seen as 8 pages of 64kB. Two ports can be used: 7 (#07) port or 15 (#0F).

Bits 0..2 - select page 0..7.
Bits 3 and 4 are ignored. Should be 0.
Bit 5 controls page size. When is 0, the selected page is seen only in upper half of address space - 32768..65535 (#8000..#FFFF). This way only 256kB are accessible, while second 256kB is hidden. When is 1 (add 32 to page number), the page is seen in whole address space - 0..65535 (#0000..#FFFF).
Bit 6 controls write-protection. To remove write-protection, add 64 to page number - values 64..51 (#40..#47).
Bit 7 selects where the SRAM is seen. When is 0, selected page is in Dock and both ports 7 and 15 can be used. When is 1 (add 128 to page number), the page is in EXROM and the port at address 7 is disabled (only port 15 can be used for next changes).

Initial value (after reset) is #00, so page 0 is selected, seen in upper half of Dock and as write protected.

Port	Value	Descritption
7 (15)	0..7	32kB in upper Dock, write protected
7 (15)	32..39	64kB in Dock, write protected
7 (15)	64..71	32kB in upper Dock, writeable
7 (15)	96..103	64kB in Dock, writeable
15	128..135	32kB in upper EXROM, write protected
15	160..167	64kB in EXROM, write protected
15	192..199	32kB in upper EXROM, writeable
15	224..231	64kB in EXROM, writeable

Files for download

68lr-003.zip 48.2kB (2006-06-04 19:44): Upgrade board v003 for 512kB SRAM, not tested.
upb-inst.txt 9.5kB (2001-08-26 16:28): [en] Description of ZXVGS UPB upgrade and its emulation.

Links to other pages

http://8bit.yarek.pl/forum/viewtopic.php?t=98: [en] Memory upgrade description.

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