KIM-1 RAM R/W pin

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GN Liu

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Nov 8, 2022, 12:42:43 AM11/8/22
to PAL 6502 computer
Hi all,

Study about the full exposed KIM-1 expansion pins for PAL-2. I'm confused about the RAM R/W pin on the expansion connector (pin Z), I did a quick look at the manuals with KIM-1and didn't find the purpose of the RAM R/W line for, just the circuit.

Does anybody knows what the RAM R/W is used for?

Thanks
Liu

Jim McClanahan

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Nov 8, 2022, 7:13:09 AM11/8/22
to GN Liu, PAL 6502 computer
On the original KIM-1, RW0 (pin 17), RW1 (pin Z), RW2 (pin X), and RW3 (pin V) are the row currently being scanned on the keyboard. (Only RW0, RW1, and RW2 are used by the actual keyboard it looks like.) They go high based on the decoded binary number sent to U45, a 74145 with ten lines out.)

Along with PA0 through PA6, you could, in theory, build an external keyboard. I'd have to dig into the ROM code, but if RW3 isn't used on the KIM motherboard, it seems like it could be used to be something like an Atari style joystick or a few special purpose keys.

Thanks,
Jim W4JBM

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GN Liu

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Nov 8, 2022, 7:21:33 AM11/8/22
to PAL 6502 computer
Thanks Jim for explaining the keyboard implementation!

But my question is on the expansion port, the upper edge connect port, maybe the RAM R/W pin is for expansion RAM operation timing I guess.

Thanks,
Liu

Jim McClanahan

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Nov 8, 2022, 8:25:42 AM11/8/22
to GN Liu, PAL 6502 computer
I see what you're looking at now. It NANDs the R/W line and the clock. A wild guess would be that it delays the write-to-RAM just a bit to ensure the address and data bus have set up and are stable. But I don't understand why you wouldn't just use fully qualified signals all the time--like your 32K RAM expansion which NANDs the clock and the R/W.

I did actually find a reference to it:


I'll have to dig into the Rockwell manual--they tended to be more detailed if I remember right. (Although it says there was an error on the AIM in implementing that line.)

Thanks,
Jim W4JBM

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GN Liu

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Nov 8, 2022, 8:47:24 AM11/8/22
to PAL 6502 computer
Thanks for the link, you're very helpful!

Of cause the PAL-2 will use the same R/W signal just like the 32K RAM expansion which NANDs the clock and the R/W which is also the KIM-1's design.

Maybe my English is not accurate, I'm just wondering what the RAM R/W pins on the expansion port are used for and why, but I think the article you pasted seems to be some kind of answer ;) 

Thanks,
Liu

John Kennedy

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Nov 8, 2022, 9:13:23 AM11/8/22
to PAL 6502 computer
Maybe this helps:

https://archive.org/details/Best_of_Micro_The_Volume_2_1979_COMPUTERIST_The_US

The new signal to G2B of the LS138 is our W RITE signal. It is produced by NANDING the "r7U" sig- nal with 0* and it is an active-low signal . On the KIM-1 it is called RAM-R/W and is available on the expansion connector. Most other 6502 systems will very likely also have a RAM-R/W signal . Its effect in Figure 1 is to inhibit the devic select pulse from the LS138 whenever the R/W line is high (during all READ instructions), but to allow the device select pulse to occur when the R/W line is low and t is high. Thus, the top LS138 in Figure 1 selects output ports only, and the device select pulse from it term- inates on the trailing edsce of the 0s, producing a logic to logic 1 transition simultaneously (almost) with t . This pulse is inverted by the LS04. Consequently, a WRITE instruction pro- duces a positive pulse at the G inputs of the LS75 whose duration is about 1/2 microsecond and whose trailing edge coincides with Z . 


GN Liu

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Nov 8, 2022, 9:33:47 AM11/8/22
to PAL 6502 computer
Hi John,

Great find! Good article explaining control signal design.

Thanks,
Liu

Dimitri

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Nov 9, 2022, 1:36:27 PM11/9/22
to PAL 6502 computer
Hi Liu

Will the PAL-2 use the same motherboard expansion board as the PAL-1? As it, will the PAL-2 expansion interface be pin-compatible with the existing extension cards?

Asking for a friend!  ;)

Thanks,
D.

GN Liu

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Nov 9, 2022, 11:35:35 PM11/9/22
to PAL 6502 computer
Hi D.,

The PAL-2 will expose all the KIM-1's application/expansion pins for a more KIM-1 compatible, so the expansion interface will double the pin numbers. 

The mother board and most of the expansion boards of PAL-1 will compatible with the PAL-2's new pins by an adapter PCB by current (non-final) design, some expansion boards, such as the second RIOT board, don't seem to be needed in the PAL-2 system.

Thanks,
Liu

Dimitri

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Nov 10, 2022, 1:45:46 AM11/10/22
to PAL 6502 computer
> The PAL-2 will expose all the KIM-1's application/expansion pins for a more KIM-1 compatible

Yay ... exposing the K[0..7] lines will simplify the address selection logic for expansion cards in the $1400-$16FF range (which is where my expansion boards live).

> The mother board and most of the expansion boards of PAL-1 will compatible with the PAL-2's new pins by an adapter PCB

And yay again ... all the current things ~will~ should continue to work!

> by current (non-final) design

And please can we have more slots and a connector for 5v regulated power supplies (eg. Molex 15-24-4745) on the backplane 'motherboard'. I am starting to get seriously worried about the current required to drive a fully loaded motherboard, so being able to an ATX power supply would be great!

Thanks,
D.

GN Liu

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Nov 10, 2022, 2:05:50 AM11/10/22
to PAL 6502 computer
>> And please can we have more slots and a connector for 5v regulated power supplies (eg. Molex 15-24-4745) on the backplane 'motherboard'.

Yes, the new motherboard will do more, and thank you for the a good idea, a connector for 5V power supply with the motherboard.

If by chance you haven't found this post about the PAL-2 design: https://groups.google.com/g/pal6502/c/6W7Q06Ls8cY

Thanks,
Liu
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