Second RIOT kit - two questions

[Magnus Olsson]

The RRIOTs in the original KIM-1 contain 64 bytes of RAM each. The single RIOT in the PAL-1 has 128 bytes of RAM which are mapped to the same memory area as the two 64 byte RAMS in the original. When I add a second RIOT there'll be an extra 128 bytes of RAM with no obvious place to go on the memory map. Is the RAM in the second RIOT not mapped anywhere, or is it accessible in another address range?

Then I'm wondering about ESD sensitivity. I noticed that on the PAL-1 itself, all the pins on the MOS circuits either have pull-up or pull-down resistors to Vcc or GND, or are connected to the TTL circuits. That should make the board fairly insensitive to static electricity, since the MOS inputs can't build up any high potentials.

But on the second RIOT kit many of the RIOT's address and data lines are just connected directly to the input connector, so they are left open when the board is not connected to the PAL-1, and it seems like this should make it quite sensitive to ESD. Has anybody had any problems with this? Is the solution to always keep it connected to the PAL-1?

[GN L]

The 128 bytes of RAM on second RIOT is invalid, its RS pin hardwired to VCC.

I put my expansion boards in a cardboard box when they are not installed on the mother board, the expansion boards seem to be safe including the second RIOT board.

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Best,
Liu

[Michael Doornbos]

I keep my KIM-1/PAL-1 related stuff in containers that have anti static foam I’ve lined them with. Got some sheets on eBay really cheap.

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[Jim McClanahan]

The MOS Technology data sheet has a note in the rating section:

"All inputs contain protection circuitry to prevent damage due to high static charges. Care should be exercised to prevent unnecessary application of voltage outside the specification range."

This same note is there for things like the 6520. It never hurts to take precautions, but from what I've seen of the whole family of chips, those designed to interface to the world are fairly robust.

Thanks,

Jim W4JBM

Link to the data sheet: http://archive.6502.org/datasheets/mos_6532_riot_preliminary_feb_1977.pdf

[Magnus Olsson]

Yes, I'm aware that more or less all MOS ICs contains some protective circuitry, but conventional wisdom back in the day at least was that this wasn't quite enough and you could still burn out the gates if you weren't careful. CMOS circuits were supposed to be better protected than the older NMOS technology. And seeing the lenghts many people go to for ESD protection it obviously can't hurt to be careful.

Of course, these expansion cards are neither very complex or expensive and the RAM or ROM circuits can be easily replaced, but the RIOT is a vintage circuit which I don't think is being manufactured anymore and it would be a shame to accidentaly damage it.

[Jim McClanahan]

Think I might have just fat fingered a message. I have a lot more experience with things like the 6520 and 6521 PIAs and the 6522 VIA. I worked as a field tech for an OSI dealer back in the 1980s and can't remember ever seeing anything that looked like damage from static charges, even in the hobby systems that would sometimes come in for repair where people had tinkered around and broke something. The only thing I remember popping frequently were the RS-232 line drivers (1488/1489s).

My impression of the 65xx input protection schemes used in the various chips is that it is fairly robust. I wouldn't push things and I agree that damaging a vintage chip that is no longer made would be a waste. Memory chips were the thing that I remember having to be more careful with.

Thanks,

Jim W4JBM

[Magnus Olsson]

Thanks. I've also never heard about anyone destroying a 65xx chip, and I've managed to avoid doing it myself, but, as I wrote, you do hear a lot of warnings about ESD.

[Magnus Olsson]

Thank you. 

Speaking of memory mapping: if I plug in both the RAM and the ROM expansions as well as the second RIOT, are there still any free addresses left in the memory space?

[GN L]

Used space:

The PAL-1 has 5K on unexpanded board ($0000-$13FF),
two RIOTs ($1700-$17FF),
KIM Monitor ($1800-$1FFF),
32K RAM expansion ($2000-$9FFF),
Jim’s ROM ($A000-$DFFF),
mirrored bottom 8K ($E000-$FFFF).


Unused space:

In theory, $1400-$16FF (768 bytes), but you cannot use these spaces directly.

So, even with some wasted space, you can consider that there is no free space within 64K.

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[Ronny Ribeiro]

I keep my PAL and expansion boards inside the anti-static bags the original parts came in. When everything is connected and grounded, I don't worry at all. I use a power supply limited to 1000 mA to have some protection in case of a short as I'm not using a 7805 voltage regulator, which confer some overload protection.
But anyways, I got some spare chips. Got some 6502s and some 6532s, and also some DRAMs. Although working perfectly, some chips were rebaged/rebranded, which made think I would pay a couple of bucks more to have good quality parts. Liu, how difficult is for you to offer some replacement chip kits on Tindie? I saw some makers of 8 bit computer kits doing it there... I would be very happy to buy replacement chips from you :)

[Magnus Olsson]

Why can't I use the address space between 1400 and 16FF? Is it because the address decoding logic considers it to be on the main board rather than on the expansion board?

It's a pity that there are no usable addresses left, because then I won't be able to add any more cards without unplugging one of the existing ones. It may be an improvement to consider for the PAL-2. Perhaps it's not necessary to let the entire range E000-FFFF mirror lower memory?

[GN L]

You’re right, you need some wire modifications on PAL-1 board to use that address space.

The address decoding on current ROM and RAM expansions is a simple design, so the mirrored memory space is some kind of waste. The PAL-2 will improve this part so that the system can provide us the full 64K space.

> On May 7, 2022, at 9:34 PM, Magnus Olsson <mne...@gmail.com> wrote:
>
> Why can't I use the address space between 1400 and 16FF? Is it because the address decoding logic considers it to be on the main board rather than on the expansion board?
>
> It's a pity that there are no usable addresses left, because then I won't be able to add any more cards without unplugging one of the existing ones. It may be an improvement to consider for the PAL-2. Perhaps it's not necessary to let the entire range E000-FFFF mirror lower memory?
>

Best,
Liu