Denial

I've had a HEScard 20 5 slot expander for several years but never had a manual for it. Does anyone have a PDF of the manual?

When using the HEScard 20 with older carts, it works as expected with only the slots "turned on" being recognized by the VIC. I haven't had any luck with modern memory and multicarts, though — the following don't work as expected:

• eslapion's Ultimate Expander 32K
• eslapion's Behr Bonz 2015
• Penultimate Cart Plus
• UltiMem

Ideally these 4 carts could all stay in the HEScard 20 and be turned on or off with the switches. That doesn't work, though. Is this because of crosstalk? Or is it something else?

akator wrote: ↑Sun Aug 15, 2021 2:52 am Ideally these 4 carts could all stay in the HEScard 20 and be turned on or off with the switches. That doesn't work, though. Is this because of crosstalk? Or is it something else?

It depends what the switches are connected to. If they just control supply of +5v (which is likely) then all the other lines will still have a load on them and could generate some form of crosstalk.

See also here: Vixen - Motherboard for Vic 20, and to quote from there:

srowe wrote:Two switches independently switch +5v to slots 3 & 4.

Mike wrote:This is actually a very bad method to deactivate the cartridges! It is generally not recommended to separate the power supply yet still connect signals to I/O of digital logic chips. That can lead to all sorts of funny/undefined behaviour of those chips or even damage them.

Interesting, thanks for the replies.

Mike, just verifying — you're saying it's a bad idea to keep multiple carts in the HEScard because of possible damage? Is this theoretical or verified?

A few hours ago I played around with the cart combinations a bit more and found the UltiMem and Penultimate Plus work correctly with the HEScard switches. Original carts from back in the day can be in the other slots and still work, but not the Ultimate Expander 32K or the Behr Bonz. But obviously, if this can damage anything I won't do it and will only use one cart in the HEScard at a time.

akator wrote:Mike, just verifying — you're saying it's a bad idea to keep multiple carts in the HEScard because of possible damage? Is this theoretical or verified?

You first need to check whether the HEScard (de-)activates the cartridges by switching the +5V power rail.

That given, there's not just (as you say) a theoretical but verified possibility of damage to the cartridges, mainly because of latch-up: when voltages are applied to (input) pins of logic chips that either exceed Vss+0.7 V or are below Vcc-0.7 V, that can trigger a parasitic thyristor present in CMOS circuits. Once triggered, that thyristor draws excess current and acts as a short as long as even a small difference voltage remains present. Normally only the complete removal of power on all pins stops this. Needless to say, a short like this - internal within a chip! - can easily destroy that chip within a few seconds.

With the supply removed, Vss of the chips effectively is 0 V, so the inputs only allow for applied voltages in the range -0.7 V .. +0.7 V. Now, the address lines, the data lines and other control signals (select, output enable, read/write) are still connected. The VIC-20 puts signal voltages outside that range on the inputs during operation (an output on high-level is anything above +2.4 V up to +5 V for TTL or NMOS). The only thing that limits the current is the TTL and NMOS circuitry normally only used inside the VIC-20. High-level outputs with TTL or NMOS only source currents in the 2-digit µA range. The latch-up nonetheless happens and pulls down all signals where it happens. If one of the outputs that 'overdrives' an unsuspecting input is itself a CMOS output, that can source a lot more current and then all bets are off.

The rule that first the supply voltages and then the signals are applied is one of the first rules learned in practical courses in digital electronics, and is motivated here.

In short: the continued use of a multiport expander that merely switches the supply voltages is no good idea. Use at your own risk. The correct method is keeping the supply connected but disconnecting all relevant control signals (BLKx, RAMx, I/Ox) and pulling them high (i.e. inactive) on the cartridge side where not connected.

As I inadvertently posted in a new post (didn't find this thread), at least for me the Penultimate + doesn't behave as expected in the Hescard 20 - it performs as expected when in an activated slot - booting to the Penultimate + menu, but when the slot is switched off the VIC 20 boots to BASIC but reports 24K of expansion RAM. When using an old school 16K cartridge, it reports the usual 3.5K when the slot is inactive, as I would expect it to. I haven't checked which lines are switched on and off by the Hescard switches yet, but I will have a look and then get back to the thread.


Edit - the push buttons just toggle the +5V line (pin 21)

doug_in_nc wrote:Edit - the push buttons just toggle the +5V line (pin 21)

Ouch. That confirms my grave concerns.

The Penultimate+ contains a FPGA to control the RAM and Flash chips inside, all in all much more delicate logic than your typical 80ies RAM expander with 6116 SRAMs. As I wrote, without a proper supply voltage, the circuitry is entitled to any kind of undefined behaviour.

That being said I also see no good reason to operate the Penultimate+ in a cartridge extender. You can select any needed RAM configuration in a menu (that includes unexpanded, i.e. "off"), and it also should provide an easy way to soft-load standard cartridge images from mass storage, making parallel operation of other ROM multi-carts like Behr-Bonz redundant.

That makes sense, I was just using it as a test cartridge rather than having any thought of long-term usage with an expander, but it does bring up another question. Even though the original 1980's cartridges are much less sensitive, would using the expander with them be doing any damage, or is it safe to continue using it with them?

Just to put that straight, for cartridge extenders that merely switch the power supply pins of the cartridges:

doug_in_nc wrote:Even though the original 1980's cartridges are much less sensitive, would using the expander with them be doing any damage, ...

Possibly, yes.

... or is it safe to continue using it with them?

No.

Thanks for the explanation, Mike. I won't be using the HEScard with multiple carts anymore. It is still more convenient than trying to get carts in and out of the back of the VIC, though.

Are there any VIC peripherals with multiple cart bays that correctly switch the carts?

Ok, so no HESware expansion boards except when using all of the connected cartridges then. Are there ones that are safe? I know the Cardco Cardboard 6 and 3S work by switching in and out the block lines, and keep the 5V line active, so presumably those are those safe?

I do have a boxed HEScard20 at my place, I'll be there tonight, I can check the manual at least and see what it says (I'm assuming there's a manual!). Or photo any pages up that revalent to confirm your suspicions.

^ Thanks, Mayhem.

I've also got a Cardco 3s. I'd be curious to hear Mike's expertise (or anyone else's) about possible damage from using that one and not the HEScard.

I opened the box, got the board in there... no manual! So either my copy is missing it, or it never came with one (which sounds unlikely). Sorry!

Yeah Mayhem, After just reading this, I went and looked at mine too... No manual either, Knowing HES though, I'm sure that it came with a Manual or at least a printed "one-sheet" set of directions/instructions. The mystery deepens...

Tony K. )

Commodore Collector/Restorer
Melbourne, Florida