Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Discussions about Sinclair ZX80 and ZX81 Hardware
tdg8934
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by tdg8934 »

Unfortunately I have a newer version 2.x board of ZXmore where the manual rotary switch and a couple of other parts are removed. Everything is done after the ZXmore boots up.


ROM Switch can be used to switch the instances manually in
position 1-7 or by control of the ZXmaster software in position 0.
Positions 1-7 can be used with ZX80 or ZX81 only (corresponding
firmware ROM programmed in flash ROM assumed) due to a
suitable default configuration.
ZXmaster can configure the ZXmore for some more firmware
ROMs like for ZX Spectrum or CP/M.
Optional for ZXmore V2.

The ROM Switch on mine was missing (or Optional as it states).


Tim
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PokeMon
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by PokeMon »

It may work when switching manually ZX81 rom with the rotary switch.
But it is then not a ZXmore but a simple ZX81 with more memory.
You can buy the switch from me (2 EUR plus shipment) if you need as it is rarely used I think - so I put this as optional now.

On the other hand, ZXpand uses IO address $07 and this would conflict with the ZXmore hardware itself (internal registers).
So at least this must be switched off, too, to get it successfully work.
You can select A3-A7 as address in general but in this case all addresses will conflict with ZXmore as all 5 bits are low for address $07 of ZXpand.
A workaround would be a pullup resistor like shown in the picture, 10k to +5V and remove of the jumper from A3 (completely).
Don't forget to put the jumper back when switching to ZXmore mode (position 0).

I never tried it but should work in general - so worth a try. ;)
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dessony
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by dessony »

tdg8934,

I can help you clearing up the confusion.... I was hooking up my original ZXmore, with its ROM switch still on, and original ZXpand together to an old monochrome NSTC CRT monitor. These 3 devices successfully were working together. :lol:

Cheers, :D

Dessony
tdg8934
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by tdg8934 »

Thank you Karl and Dessony.

I found some 4.7k resistors (no 10k) 1/8w. Use 1 4.7k or 2 in serial for 10k?

Also is do I have to unsolder the resistor (or use a switch in between) besides using / not using the A3 jumper?

Tim
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Paul
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by Paul »

Two 4k7 in serial please. One will also work but two give less "stress" to A3. And no switch or desoldering is required for use of the jumper.
A switch CAN be used with the middle pin to the top position of the jumper, one to the lower position of the jumper and 5v via 10k resistor to the other side of the switch.
So either 5v OR A3 are connected to the selector.
In the original hint, when using the jumper, A3 is "stressed" with the 10k resistor.
A3 can easily handle this though.
The description of the use of the switch was only for explanation, not necessary at all.
Hth
Paul
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1024MAK
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by 1024MAK »

The 10k resistor (or in your case, two 4.7k resistors wired in series) wired between a digital logic line and a supply such as +5V, is known as a "pull-up". When the jumper is removed, it maintains a logic high (logic one) to the digital logic line. But when the jumper is fitted, it's value is high enough that it does not interfere with normal operation. For use with the ZXpand, the jumper is removed (or plug it in using one pin only, with "half" of the "jumper shunt" overhanging in the air). Connect it as you currently have it for normal ZXmore operation.

There are two ways of using a switch.

The method described by Paul. I can expand on his description and give some more detail: this requires a single pole change-over switch (also known as a SPCO or SPDT). This has three pins. The middle pin is the moving common contact and should be wired to the jumper pin that connects to A3 (the logic line to the chip on the ZXmore). One of the other pins connects to the other jumper pin. The remaining pin connects to the +5V supply via a suitable resistor. You should NOT connect a "jumper shunt" link.

The other method uses a ON/OFF SPST (single pole, single throw) switch. This type only has two pins. One pin goes to one pin of the jumper. The second pin goes to the other pin of the jumper. The 10k resistor (or in your case, the two 4.7k resistors connected in series) is fitted exactly the same as if you were using a "jumper shunt", as shown in the photo posted by Pokemon. The switch directly replaces the "jumper shunt" link.

Mark
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tdg8934
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by tdg8934 »

Thank you Paul and Matk! Excellent write ups. Fortunately I have a degree in Electrical Engineering but working out of the field as a Systems Engineer doing system testing.

Since I didn't know the ZXmore board I just wanted to know if it had to be a "hard" pull up or if a soft one would be good enough including if it was necessary for the resistor removal each time. Since I don't need to remove the resistor each time switching it from ZXPand/ZXPand+ use with ZXmore, the jumper insertion and half hang over method will be my substitute for a switch as it's easy access and small being out of the way that a switch might lack.

I will try this out shortly and report back.

Thanks again - Tim
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1024MAK
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by 1024MAK »

Ahh, it's sometimes difficult to guess at someone's knowledge or skill level on a forum. I try to give descriptions and help in a manner that helps the person asking the question and anyone else who reads this thread.

The ZXmore uses modern CMOS chips, hence a "soft" pull-up.

Mark
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tdg8934
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by tdg8934 »

Isn't a soft pull-up a 4.7k and s hard being 10k?

Tim
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1024MAK
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Re: Has anyone been sucessfull interfacing ZXmore with ZXPand or ZXPand+ ?

Post by 1024MAK »

Well, depends on your terminology...

I call higher value resistors soft pull-ups, as they supply less current.
Whereas a hard pull-up using lower value resistors is "harder" for a chip to pull down to a logic low / logic zero...

Mark
ZX81 Variations
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ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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