Yet another ROM adapter

Discussions about Sinclair ZX80 and ZX81 Hardware
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Paul
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Re: Yet another ROM adapter

Post by Paul » Wed Dec 20, 2017 9:00 pm

sirmorris wrote:
Wed Dec 20, 2017 8:56 pm
rune wrote:
Wed Dec 20, 2017 6:37 pm
Postage to UK is a very reasonable $2.33 - Probably as cheap or cheaper than buying a bulk lot and re posting within the UK.
Agreed.
Do you order one for me as well?
In theory, there is no difference between theory and practice. But, in practice, there is.

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sirmorris
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Re: Yet another ROM adapter

Post by sirmorris » Wed Dec 20, 2017 9:02 pm

I'm having trouble .. there doesn't seem to be a way to select the item :P
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

rune
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Re: Yet another ROM adapter

Post by rune » Wed Dec 20, 2017 10:14 pm

Paul & Charlie

Sorry, I only ordered two as I hadn't heard from anyone and I wasn't sure if Id have time tomorrow.

Drop a line to Dan, he replies quickly and its an easy purchase.

Dave

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sirmorris
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Re: Yet another ROM adapter

Post by sirmorris » Wed Dec 20, 2017 10:33 pm

Done. Nicely!
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

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gammaray
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Location: Texas

Re: Yet another ROM adapter

Post by gammaray » Thu Dec 21, 2017 12:25 am

Leave one for me I have been sick and unable to order one... Got to get to bank blah blah blah

Please :(
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

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mooredan
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Re: Yet another ROM adapter

Post by mooredan » Thu Dec 21, 2017 4:38 am

gamma, send me your paypal email address and I respond with an invoice. It's the last one available.

Looks like there's enough interest to order another batch, ....but I'll wait for feedback for any potential design changes or improvements.

I'm on the verge of routing a wire from A13 over to the jumper to test addressing 16kB at a time, been busy writing some code to go in there.

Selecting 8kB banks at a time is working just fine.
Dan Moore
Portland, Oregon, USA

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mooredan
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Re: Yet another ROM adapter

Post by mooredan » Thu Dec 21, 2017 7:40 am

I should have used a right angle style jumper for the A13 line. ...and probably used two resistors, instead of one, on the A13 tie up/down. What are we looking at, 10 uA max through a 1kohm = 10mV drop --- yeah probably OK, but not having the resistor in the path would just make me feel better.

Anyway, one solder job and we're in business. We now have the whole lower 16kB available to us.

The convenient spot to pick up A13 is right by the mounting hole:

Image

...and here's with the jumper and ROM adapter in place:

Image

OK, does it actually work:

Well, I'm working on this program:
Image

Here's a small BASIC program to see what the first few bytes are in the "shadow" area:
Image

...I'll let you do the decimal <--> hex conversion.
Image
Dan Moore
Portland, Oregon, USA

McKlaud
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Re: Yet another ROM adapter

Post by McKlaud » Thu Dec 21, 2017 7:49 am

Very nice and useful adapter. It looks I'm late and no single board left One thing that I am not convinced with are surface mounted pin headers.
Claudius
----------

dessony
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Location: Indiana, USA

Re: Yet another ROM adapter

Post by dessony » Thu Dec 21, 2017 10:49 pm

McKlaud and everybody,

I quoted you, "One thing that I am not convinced with are surface mounted pin headers."

I just received my order from Digi-key. I have a piece of a MPH100IMP40M-G-V-SM-ND in according to mooredan's own website. http://dlmeng.suncup.net/zx81-ts1000-rom-adapter-pcb/ I looked at the shape of male pin headers' contacts, they are round! :D :lol: Just use a precision machine tuned socket when you want to solder the headers onto the board.

Please mind the resistors' size, which is 2mm lengthwise x 1mm wide, when you are soldering them onto the board. :!:

Cheers,
Dessony

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mooredan
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Re: Yet another ROM adapter

Post by mooredan » Fri Dec 22, 2017 1:22 am

...or just remove the ROM socket from the ZX81 board altogether and solder the adapter board directly in. If you can program an EPROM, there's really no need to ever have to remove the adapter -- that's what's the ZIF socket is for.

Yeah the 0805 resistors are about the limit for comfortably soldering by hand. I pre-fill the pads with a very small piece of solder that I cut off the spool with an X-acto knife. ...then use some tweezers to apply some downward pressure on the resistor while just touching the pad with the iron.
Dan Moore
Portland, Oregon, USA

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