ZXblast - ZX81 memory extension plus USB

[PokeMon]

So now stable operation after weeks of testing it and finding/solving the bugs. ZXblast ist nearly ready to be sent but next week I have much work at work (sounds funny ) and I have to create a documentation for it. So will post further information in the next days and could be sent from 09/10th of novembre. So be prepared - it's coming now very very soon. From now on only administrative delays.

[1024MAK]

Hi PokeMon

Good news (I think)!

I hope "real life" work doesn't keep you too busy.

Mark

[mrtinb]

I'm ready

[blittled]

I'm looking forward to the release too! Right now I'm resisting the urge to buy a ZX-PAND. The ZX-Blast looks like it has a lot of interesting features and potential to open USB technology to the ZX81!

[PokeMon]

So planned to release the ZXblast officially this weekend but unfortunately there is a bereavement not in my family but in the narrow circle of friends which implicates some stress at the work as well - so stay tuned with a delay of approximately one more week to meet all necessary arrangements. Thanks for your patience.

[1024MAK]

Take you time Karl

I sure everyone will understand.

Mark

[Moggy]

+1
My condolences to you Karl also.

[blittled]

Take care Karl and get everything worked out. We'll be patiently waiting.

[gammaray]

[PokeMon]

So the ZXblast is finalized now and here is some technical information about it:

In general it is a configurable memory extension with a USB flash media interface for loading and storing programs and/or data. It contains different pages of flash rom and ram which can be combined to instances like done with the ZXmore. The difference is, that there is no multi tasking feature embedded as it doesn't make sense to make the ZX81 slower than it is in general. But it is easy to change different in parallel started programs by double shift key plus 1-7 (up to 7 instances/programs with 512k RAM) while only the active program is executed, all others are halted in the background and are continued when activating them.

It is possible to choose any configuration of memory pages but the memory configuration is the same for all instances. You can activate RAM in 8k-16k area easily and in fact you can choose RAM or ROM for every 16k page, even in classic ROM area 0-16k for experiments with ROM changes or optimizations. So for all areas 0-16k, 16-32k, 32-48k, 48-64k can be choosen either ROM or RAM. Additionally it is possible to switch of RAM/ROM partly for the sections 8-16k, 32-48k and 48-64k to hold this free for additional hardware providing RAM or ROM like the ZX Chroma or other interfaces. There is another feature to mirror the 0-32k address space like the original hardware does. This way you have 0-16k ROM (or 0-8k ROM and 8-16k RAM) and 16-32k RAM while it is mirrored to 32-48k (ROM) and 48-64k (RAM). This is a compatibility feature for some special software/hardware.

Finally it is possible to use banking/paging mode which allows, to use nearly all of the 512k inside a single instance. Unfortunately there was never a memory mapping or memory management standard from Sinclair, so it is hard to find software using this feature but possible to develop own software. The paging size can be chosen with 8k or 16k window and up to 32 pages and the ram page can be used in any memory area in 8k steps (default 16k window at address $C000-$FFFF when activated).

This memory overlaps fully with the instance memory but it is easy to configure as it is used from the back. If usage is restricted to 256k for paging than the first 3 instances can be used in parallel to paging mode. Maximum usage would be around 448k with one program instance. Due to it's overlapping it is also possible to access memory of other instances, manipulate data and investigate programs when using a disassembler in another instance. This is more developer mode action. Due to the lack of existing programs and existing paging mechanisms in the past this is useful for software developers only, I think.

The flash ROM allows to use different firmware ROMs and/or additional drivers loaded in area 8-16k or 32-48k. The type of ROMs are limited to ZX81 charset as this is deeply grounded in the system with overdriving rom address lines from the ULA. This is a big difference to the ZXmore. It is not possible to use ZX80 or H4TH (Husband Forth) as they have a different charset. All rom's based on the ZX81 charset can be used (default address $1E00). There is by the way a patched H4TH version existing which can be used with the ZXmore in the meanwhile but need adaption for load and save features. This version would run even with ZXblast but doesn't show valuable screen contents as the charset differs quite much.

So here is a technical summary of the features:

Features:
=> 512k Flash ROM divided in 8x 64k (7 instances plus ZXblast control instance)
=> 512k RAM divided in 8x 64k (7 instances plus ZXblast control instance)
=> USB flash media for LOAD and SAVE programs an/or data
=> memory layout free configurable with using RAM or flash ROM for the memory areas 0-8k, 8-16k, 16-32k, 32-48k, 48-64k
=> banking/paging mode with 8k or 16k width and up to 32 pages with freely configurable window location from 0-64k in 8k steps
=> storing and loading of complete instances (all RAM) at any time with running programs, to be continued later at interrupted point (useful feature for games and other which do not allow to be saved when started)
=> complete system backup and restore of all instances when shutting down and starting up system