Question #2: EXEROM and tape loading

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Bill B
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Re: Question #2: EXEROM and tape loading

Post by Bill B »

Don't know. Probably would not work.

Could use ROM 6 instead, but that would need some extra logic to decode the ROM 6 signal.
Martin A
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Re: Question #2: EXEROM and tape loading

Post by Martin A »

From what I've seen in photos the chip select for the piggyback rom is "yellow wired" to GROM using a convenient via to anchor it.

That's why the V1.1 Magrom needed an extra chip, to decode ROM 6, compared to the original that uses GROM, to make it work with language roms.

As far a CFX goes, that only decodes 2 rom images, 4 and 5. As only one rom select line, R0, is connected to the flash rom, it's not expandable.

CFX-II on the other hand does have R0 and R1 connected to the flash so that can decode up to 4 rom images (4 to 7 or possibly 4,5,2,3 in that order) if the CPLD was suitably set up. (Right now I can't rememebr if it's currently programmed for 4,5,6 or just 4 & 5),

The actulal size of the flash chip isn't an issue, both boards were designed to take a 32 pin 128k x 8. Flash of that size being mugh cheaper than the physically smaller 28 pin 32k eeprom!
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1024MAK
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Re: Question #2: EXEROM and tape loading

Post by 1024MAK »

The other problem, is that fitting a modern EPROM / EEPROM or flash ROM to a MTX board, requires wiring changes to the board. Which is further complicated by there being two different main boards in widespread use. One of which uses three ROM chips, and one of which uses only two ROM chips,

So not so simple to do...

Mark
kokkiklhs
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Re: Question #2: EXEROM and tape loading

Post by kokkiklhs »

Oh, thank you all for your time and patience to give such detailed answers... So the machine is "crippled" and this is because of the ROM original structure... Very sad to realize that...
Well, this reminds me of the Camputers Lynx with the painfully slow BASIC due to its peculiar video RAM handling techniques... I guess all these are SERIOUS reasons to understand the merchandising failure (and on the other hand the success of machines like the ZX range or the CPC)... NOT user-friendly at all and NOT for the average low-budget kiddo user of the era to cheaply and easily experiment with...
Anyway, I still like the MTX, but I know now that I wouldn't buy it as first and only computer back then, even if I had the chance! :D
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1024MAK
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Re: Question #2: EXEROM and tape loading

Post by 1024MAK »

I think your comments are a bit harsh. The ZX80 and ZX81 did not have any ability to load code or data files. You could only load them from BASIC as part of a normal program LOAD. We now know of three different official ROM versions, the first one having a bad mathematical bug. The second version also having a bug, that was fixed in the third version. But some bugs still remain in this third and final official version.

The Commodore 64 with its serial IEEE-488 bus used primarily for its disk drive system was speed limited due to to a hardware bug in the VIA 6522 chips used in the VIC-20 computers and in the 1540 and 1541 disk drives. Hence the serial IEEE-488 bus interface having to operate in bit bashed mode as opposed to using hardware to do the parallel to serial and serial to parallel conversion.

And the Commodore 64 has a version of Microsoft BASIC with no additions to handle the machines graphics and sound features.

The ZX Spectrum ROM is unfinished, and has plenty of bugs. Plus a redundant ZX81 routine. And it has no random access data file system for tape like some other machines. Further it’s ROM code is not exactly well organised either. And the 128K machine adds various new bugs, plus it’s BASIC is slower as it has to keep swapping between ROM banks.

Even the expensive Acorn BBC Micro started off with the buggy OS 0.1 ROM and it took a while before OS 1.2 with most of the bugs squashed and the required features included became available.

Most of these machines have mask ROMs and either these were soldered in, or where sockets were provided, because they were designed for mask ROM chips, the pin-out is not compatible with 27 series EPROM chips.

Of the machines I mention above, only the Acorn BBC Micro and the ZX Spectrum 128K can take a 27 series EPROM as a simple plug in replacement.

Mark
stephen_usher
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Re: Question #2: EXEROM and tape loading

Post by stephen_usher »

Indeed. At the time loading data directly into addresses via BASIC wasn't generally a thing, nor was making the BASIC extendable. Hind sight from 40 years in the future is a wonderful thing.

I guess that you could write an assembler routine, using the built in assembler, to use the tape interface to load and save data blocks but without jump points into a set of tape routines in ROM you'd have to write the whole of the tape data handling yourself. I guess that you could put it into a "sideways ROM" and switch over to that in an assembler routine, but there was never a "sideways ROM" card available for the MTX.

Who knows what would have happened if the machine had taken off and there had been a flourishing 3rd party hardware ecosystem, it would probably have been very different.
Martin A
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Re: Question #2: EXEROM and tape loading

Post by Martin A »

That's a bit of a jump from "It's not practical to re-write the OS" to "the machine is crippled."

Using Jon's systems as an example (viewtopic.php?f=10&t=505) How many pople who've just spent £275 on a vintage system in A1 condition would be willing to take a knife to the circuit board? Because that's what's required to replace the ROMs on a -05 board. The -04 board wold "only" require links changing to support (e)eproms but since they're solered in, it's still surgery.

And yes I have done that http://primrosebank.net/computers/mtx/r ... air_ma.htm note the yellow labels on the eeproms in the main photo. But then I was repairng a board that had issues, and already had cut tracks from the factory fit of 2532 eproms, there was nothing to loose by fitting 2864 eeprom and plenty to gain (no more purple panel!). Most systems aren't like that, thankfully.

The MTX has namy advantages over systems of the era. How many of its rivals had:
A built in assembler
A build in disassembler/front panel
Up to 512k memory for Basic
Over to 4 megabytes of rom space defined (8k os, 8 x 8k Paged rom slots, of which slots 2 & 3 allowed for 256 sub pages of 8k)
That gorgeous aluminium case

Yes, the OS is "messy" from the efforts so squeeze everything in. The relaiance on LET is a pain. The keyboard doesn't like long periods of inactivity. It's a sytem of it's age. But it's still one of the better systems of that age.
Bill B
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Re: Question #2: EXEROM and tape loading

Post by Bill B »

Also, although the ROMs are cramped, they also provide a lot of flexibility. I count 12 places in the system variables where it is possible to insert code to modify or extend the behaviour of BASIC.

How many other machines of that era provide that level of flexibility?
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gunrock
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Re: Question #2: EXEROM and tape loading

Post by gunrock »

We haven't even mentioned microdrives or the Sinclair QL; when it comes to rushed gestation and awkward births. I was a Commodore user in that era and the Memotech oozes class and bridges the gap between home computer and serious computer way better than say, the Commodore 128.
kokkiklhs
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Re: Question #2: EXEROM and tape loading

Post by kokkiklhs »

I agree with all your comments above, the MTX are superb machines for their era, but since I knew little to nothing about them, I was not expecting such a serious omitment as the inability of loading blocks of code from tape. I think that such a thing was essential for the average user back then...
Of course all rival machines had their flaws as well, but this was a serious-profile and expensive machine and it's a pity that apart from its fabulous advantages and novelties, it also had some severe dark spots...
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