Author Topic: Where to buy / any downsides to Parados ROM?  (Read 9233 times)

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Offline bleeper

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Where to buy / any downsides to Parados ROM?
« on: 15:52, 11 June 10 »
I've been reading the Wiki and this seems like a good ROM to have in place of Amsdos.
 
However, I don't have the means to produce one myself so would like to buy one, and was also wondering if there is any downsides to using Parados? Is compatibility identical?
 
 

Offline Bryce

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Re: Where to buy / any downsides to Parados ROM?
« Reply #1 on: 16:26, 11 June 10 »
The ParaDOS ROMs can be downloaded from the Wiki, then you just need to flash them to a ROM. Have you checked whether someone local could burn it for you? Do you have a suitable ROMBoard or were you going to permanently replace the internal AMSDOS ROM?

Bryce.

Offline bleeper

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Re: Where to buy / any downsides to Parados ROM?
« Reply #2 on: 17:08, 11 June 10 »
No I hadn't checked yet  :-[  it's just a standard EEPROM required then?
 
I don't have a ROM board I was just hoping I could replace the existing AMSDOS which is why I wondered if there were downsides to this... aside from being able to run as 'stock'.


Offline bleeper

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Re: Where to buy / any downsides to Parados ROM?
« Reply #4 on: 14:03, 12 June 10 »
Thanks eliot that looks good, never thought of eBay!  :o
 
:: I'm still wondering though, if I actually need to have it switchable, or if Parados will perform anything Amsdos can?

Offline OCT

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"Piggyback" ParaDOS/AMSDOS switch
« Reply #5 on: 22:15, 12 June 10 »
I'm still wondering though, if I actually need to have it switchable, or if Parados will perform anything Amsdos can?
While ParaDOS excellently does everything like AMSDOS and much more, some software may malfunction e.g. due to slight differences in memory use.
However, you only have to carefully lift one pin (the so-called "chip enable") of each the ParaDOS and the original ROM to fit a double-toggle switch between the two (certainly someone has already made and uploaded schematics for that) - the rest of the ParaDOS EPROM's pins can be soldered "piggyback" on top of the AMSDOS ROM.

Offline eliot

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Re: Where to buy / any downsides to Parados ROM?
« Reply #6 on: 23:28, 12 June 10 »
piggyback soldering : you can do the same with 2 different CRTC...  (a little bit off-topic, I admit  :P

Offline Bryce

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Re: Where to buy / any downsides to Parados ROM?
« Reply #7 on: 14:51, 13 June 10 »
Piggy-backing ROMs is such a messy solution, I much prefer using an external ROMboard which can map ROMs to 0/7 etc, to override the internal ones.

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Offline TFM

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Re: Where to buy / any downsides to Parados ROM?
« Reply #8 on: 23:12, 23 June 10 »
I've been reading the Wiki and this seems like a good ROM to have in place of Amsdos.
 
However, I don't have the means to produce one myself so would like to buy one, and was also wondering if there is any downsides to using Parados? Is compatibility identical?

The biggest problem (and IMHO a real pitfall) of Parados is, that it doesn't support the Vortex format. Well, why is this a problem? The Vortex format is THE standard format for any kind of Vortex drives or Dobbertin drives. And they are commonly used in germany.
 
Instead of Parados I use the XD-DOS, it contains a lot of usefull additional commands, supports even the HD20 hard-disc and naturally the Vortex format.
 
 
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Offline Executioner

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Re: Where to buy / any downsides to Parados ROM?
« Reply #9 on: 03:22, 24 June 10 »
Instead of Parados I use the XD-DOS, it contains a lot of usefull additional commands, supports even the HD20 hard-disc and naturally the Vortex format.

Yeah, it supports the German Vortex format and the HD20, but does it support DS80 Data/System and ROMDOS formats which are the most common outside Germany.

Offline TFM

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Re: Where to buy / any downsides to Parados ROM?
« Reply #10 on: 22:59, 27 June 10 »
Yeah, it supports the German Vortex format and the HD20, but does it support DS80 Data/System and ROMDOS formats which are the most common outside Germany.

What is "DS80 Data/System and ROMDOS formats" ??? :o  Does somebody outside the UK know them???
 
However, XD-DOS f.e. also supports the 0.7 MB Data and the 0.7 MB System format, if you're talking about this?
« Last Edit: 19:31, 22 July 10 by TFM/FS »
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sixonetwoeight

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Re: Where to buy / any downsides to Parados ROM?
« Reply #11 on: 20:35, 21 July 10 »
Does anyone know what's the chip enable pin of AMSDOS / Parados? Piggybacking might be a messy solution but it's also cheap :-)

Offline Devilmarkus

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Re: Where to buy / any downsides to Parados ROM?
« Reply #12 on: 21:10, 21 July 10 »
Does anyone know what's the chip enable pin of AMSDOS / Parados? Piggybacking might be a messy solution but it's also cheap :-)

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sixonetwoeight

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Re: Where to buy / any downsides to Parados ROM?
« Reply #13 on: 22:12, 21 July 10 »
yeah my PC is behaving strange ... this is my evil twin!  ;D

Offline Bryce

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Re: Where to buy / any downsides to Parados ROM?
« Reply #14 on: 22:48, 21 July 10 »
Hi Evil Twin,
       There's no Chip Enable, but they do have a Chip Select (Pin 20) and an Output Enable (Pin 22). For true compatibility, you'll need to use a 2 pole switch to switch both signals between Original and piggy-backed chip, all other pins can be directly connected in parallel.

 Bryce.
« Last Edit: 22:51, 21 July 10 by Bryce »

Offline archcosmo

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Re: Where to buy / any downsides to Parados ROM?
« Reply #15 on: 13:27, 24 July 10 »
took this screenshot from Amstrad Techical Manual #2 - pin 13 is meant to be the right one for the piggyback method

but I prefer to make my own eprom and use a switch to enable Parados - took me a while to desolder the existing chips before installing eprom sockets, but it looks much more tidy ;-)

EDIT: photo 3 shows the reset button, parados switch, and A/off/B switches for the internal 3" drive, and for external floppies (DS 4 - 1, or 3 - 0 if you prefer)
« Last Edit: 13:31, 24 July 10 by archcosmo »

Offline OCT

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Re: AMSDOS and ParaDOS crammed into one single EEPROM
« Reply #16 on: 16:09, 24 July 10 »
I prefer to make my own eprom and use a switch to enable Parados
From your second image I gather you are using an EPROM of double capacity but identical pin count, probably switching an address line between GND and +5V to toggle the appropriate "half" ?
Could you provide some more details on this for the readers who do not have ParaDOS installed (piggyback or otherwise) yet?
« Last Edit: 16:12, 24 July 10 by OCT »

Offline xesrjb

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Re: Where to buy / any downsides to Parados ROM?
« Reply #17 on: 17:31, 24 July 10 »
I solder an 27512 in my CPC:1. AMSDOS;2. Vortex 2.11;3. DDOS (720kB Dos from Dobbertin, but the CPC has to run as a 464 not as a 6128),4. Parados 1.3 (Patched Parados 1.1 that run in a  2 x 720kB Mode.

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Offline OCT

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Re: Where to buy / any downsides to Parados ROM?
« Reply #18 on: 09:51, 25 July 10 »
I solder an 27512 in my CPC:1. AMSDOS;2. Vortex 2.11;3. DDOS (720kB Dos from Dobbertin, but the CPC has to run as a 464 not as a 6128),4. Parados 1.3 (Patched Parados 1.1 that run in a  2 x 720kB Mode.

xesrjb
As it won't necessarily be obvious to everyone who comes across this thread (without http://www.datasheetcatalog.org/datasheets/120/227190_DS.pdf at least), I suppose in addition to archosmo's A14 (pin 27 right next to the top left +5V VCC) in his second picture posted above, you are probably using A15 (pin 1 bottom left), also pulling it to either GND (pin 14 VSS bottom right) or VCC as a ROM bank toggle, having burned the EPROM from all 4 ROM images concatenated into one "big" file of 65536 bytes?

BTW, I have seen the question how to patch ParaDOS into starting up with different drive settings (such as dual-head double-density) asked before on this forum (or was it only on SymbOS?). For the record, ;) could you (or diff :)) specify which locations you have modified (especially in case the ROMs do have a checksum) on which version of ParaDOS?
« Last Edit: 10:57, 25 July 10 by OCT »

Offline OCT

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Re: Where to buy / any downsides to Parados ROM?
« Reply #19 on: 10:46, 25 July 10 »
       There's no Chip Enable, but they do have a Chip Select (Pin 20) and an Output Enable (Pin 22). For true compatibility, you'll need to use a 2 pole switch to switch both signals between Original and piggy-backed chip, all other pins can be directly connected in parallel.
Wait a minute about "There no a spoon."
"There no a spoon." ;)
The datasheets do say (with respect to Pin 20): "both [control functions] must be logically active in order to obtain data at the outputs. Chip Enable (E) is the power control and should be used for device selection. [...] Data is available at the outputs after delay of tGLQV from the falling edge of G [i.e. Pin 22: Output Enable], assuming that E has been low and the addresses have been stable for at least tAVQV-tGLQV."
Not sure why G would have to be switched as well even though the disabled ROM's data bus is defined to go tri-stated while E is high, i.e. shouldn't garble communications with the active ROM.
« Last Edit: 10:50, 25 July 10 by OCT »

Offline archcosmo

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Re: AMSDOS and ParaDOS crammed into one single EEPROM
« Reply #20 on: 11:21, 25 July 10 »
Hi guys

yes, you're correct, I've used a 27c256 (32KByte) Eprom for this mod - I got the inspiration not only from seeing the finished result linked to that ebay auction in the first post, but also from some info I came across in Amstrad Technical Manual #1 that describes installing a 32k eprom into a Romboard. like you state above, pin 27 (A14) is set to 0volts or 5volts via an SPST toggle switch wired to pin 28 (5volts) on one leg, and pin 14 (GND) on the other leg

in order to program a 32K eprom you'll need to join the BIN/ROM files together, but as well as that, the Eprom files I'd downloaded also had the Amsdos file header which needs to be removed so that the programmed eprom will fit into exactly 32KB. the first 128bytes was cut from the start of the file using a file or hex editor to do it so the file is exactly 16Kbyte (16384bytes). I've used Hex Workshop v5 in the past and more recently Winhex to trim the file and then subsequently join them both together. there's a CPCWiki article which describes programming with Williem Eprom programmer (I've got the most recent variant:PCB version 5) and joining the files together from the windows command line, so I won't repeat that info here.. :)

you'll need to allow a couple of hours to desolder the eproms and prep for soldering in the sockets.. desolder braid and a soldering iron will remove it, but you'll also need a small pair of pliers to wiggle any chip legs that are stuck in their holes whilst heating it with the iron before chip extraction. as I like my soldering work to be neat and tidy, and as the desolder braid leaves a lot of flux on the PCB, I used some isopropyl alcohol and cotton buds to dissolve and remove the remaining flux on the top and bottom... but not too much, as IPA will also dissolve some of the PCB varnish on top of any nearby tracks (potentially exposing them to corrosion in the future!)

then you'll need to solder the hookup wire from the switch to the eprom. pin 14 (GND) of the chip is wired to one of the outside pins of the toggle switch. pin 28 (+5V) is wired to the other outside pin, with pin 27 attached to the centre pin of the switch. the screen shot (attached) should help here

installing the socket should be straightforward - depending on the type, you might find that the legs will need to be bent outwards a little so that the legs make it through the holes to the back of the PCB.

hope this helps explain the unclear parts of the my photos from earlier.. :-)

BOM:
27c256 eprom (erased)
SPST mini toggle switch (on-on type)
hookup wire (x3) about 30cm long to allow for sufficient room if you take the keyboard apart later
2mm heat shrink tubing (install it on pin 27 of the eprom)
28pin eprom socket (I used machined pin sockets, as cheaper sockets would have their metal pins pushed back once you push them down on to the PCB)

tools I used
soldering iron (40watt or so, fine tip will help too)
desolder braid (solder sucker tool is handy too)
lead free solder
power drill
drill bit that is the same diameter of the switch barrel
vernier calipers
pliers
UV eprom eraser

EDIT - fixed what was attached to my message.

From your second image I gather you are using an EPROM of double capacity but identical pin count, probably switching an address line between GND and +5V to toggle the appropriate "half" ?
Could you provide some more details on this for the readers who do not have ParaDOS installed (piggyback or otherwise) yet?
« Last Edit: 11:38, 25 July 10 by archcosmo »

Offline OCT

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Re: AMSDOS and ParaDOS crammed into one single EEPROM
« Reply #21 on: 12:46, 25 July 10 »
Many thanks for your very detailed description. :)
I for one resorted to the piggybacking approach (lifting only Pin 20) fearing that the CPCs' aging hardware might not take major desoldering stunts lightly (IIRC even from 15 years ago when I did this, albeit without the clever "bank-switching" by repurposed address lines inside one ROM chip).
UV eprom eraser
may be hard to come by, but in summertime about a week's exposure to direct sunlight (not behind ordinary windows which will reflect most of it at UV wavelengths) should also do the trick, with the IC's legs in conductive styrofoam to avoid any static charge.
The rays of a tanning booth are not sufficiently "hard" AFAIK, however...
« Last Edit: 00:42, 06 August 10 by OCT »

Offline OCT

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BTW without having looked into the actual wiring, I wonder if there's a way for the CPC to use actual 27512s plugged in place of the usual 16+32kByte ROMs even without a hardware switch, i.e. to toggle both A14 and A15 by itself in software?
At first glance from http://cpcwiki.eu/imgs/7/79/CPC6128_PCB_Bottom_%28Z70290_MC0020B%29.jpg pin 27 seems to be pulled to +5V (expectedly) on the AMSDOS one of the ICs and pin 1 floating on both, but the CPU and its address bus aren't far away if these could be put to any use (without conflicting with anything else?).
Yes, internal SymbOS/FutureOS + room for 3 more ROMs to spare (i.e. the original ones, which would need a hardware switch then) is what I'm thinking of...
« Last Edit: 13:19, 25 July 10 by OCT »

Offline TFM

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Re: Where to buy / any downsides to Parados ROM?
« Reply #23 on: 23:57, 05 August 10 »
While Tony tested my Amsdos/Basic version of the SF2 ROManager he found another "fact" about Parados, that should be mentioned at least, since it can bring some confusion...
 
Usually every expansion ROM (but neither BASIC nor AMSDOS) has a checksum in address &FFFF, this 8 bit checksum is calculated in every ROM in the same way: Just by adding the contents of the bytes from &C000 to &FFFE.
 
Well, Parados has no such checksum :-( This is not a problem with emulators, but it can become a problem with the SF2 (in case of a low battery) or when using an EPROM.
 
The solution: You can use ROManager to install the checksum correctly (it's &26 btw...). And you really should do that. Else you will not see if the parados gets corrupted due to a faulty eprom or a weak battery.
 
BTW: ROManager doesn't change the checksum of ROM 0 and ROM 7, because they are usually occupied by BASIC and AmsDOS, and they must remain as they are.
« Last Edit: 00:02, 06 August 10 by TFM/FS »
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