PAL-2 Dip Switches / Memory Config

[Jeremy Starcher]

I am not as great at reading schematics as I should be.

Is there an Explain Like I'm 5 version of what the various DIP switches do?

[GN Liu]

The PAL-2 has a full 64K address decoder onboard, while the KIM-1 has only a 5K onboard address decoder for expansion. These two DIP switches on the PAL-2 are designed both to expand the KIM-1’s RAM and to maintain compatibility with its basic configuration.

On the PAL-2, the 4-bit DIP switch enables the onboard K1 to K4 RAM spaces, with each bit controlling 1K of memory. The K1 to K4 naming follows the definitions in the KIM-1 user manual, covering the address range from $0400 to $13FF. If all four DIP switches are set to ON, the entire 5K RAM space becomes available to the system.

The 8-bit DIP switch controls the “big segment decoder,” with each bit corresponding to an 8K memory block. These blocks range from 8K0 to 8K7, with 8K0 ($0000 to $1FFF) being the KIM-1’s default occupied address space. Since the PAL-2 is a KIM-1 replica, if you want to use it as a KIM-1 system, 8K0 must be set to OFF to allow the onboard KIM-1 logic to function. However, if you’re building a completely new system on the PAL-2, you can set 8K0 to ON to bypass the KIM-1’s onboard logic for the lowest 8K of memory.

The 8K1 block starts at $2000, controlling an 8K space beyond this address, and so on. If a bit is set to ON, the KIM-1 system will be able to access the corresponding address space, which will function as RAM. If a bit is set to OFF, the KIM-1 system will still work, but with reduced available address space. When performing expansion or add-on modifications on the PAL-2, you may need to disable certain address spaces to prevent the onboard logic from accessing the RAM chip.

The 8K7 block, representing the highest 8K memory segment, offers additional flexibility on the PAL-2. If 8K7 is set to ON, you can choose how to use this space—either as RAM or ROM—by adjusting the 8K7 SEL switch. For example, if you write a program (such as a tiny OS for the KIM-1) and burn it onto a ROM chip—similar to the well-known Jim’s ROM (but smaller)—you can connect the ROM to the PAL-2 (with some additional hardware, which is still under development). To boot from your ROM chip, use the VECTOR SEL switch to select ROM, allowing the system to retrieve the top three vectors from the ROM chip instead of the onboard KIM-1 ROM.

I hope this explanation makes sense!

[Jeremy Starcher]

That makes total sense!

Thank you and thank you. Makes total sense.

[Jeremy Starcher]

I'm seeing a bit of of a behavior difference between the PAL-1 and the PAL-2 that I'm trying to understand.

I take the PAL-1 with the 32K RAM expansion.

I flip the switch on the PAL-1 to use the extended/offboard memory

I set memory address '0000' to '77'
I set memory address '2000' to 'AA'

Address '2000' displays 'AA'
I flip the selector switch.
Address '2000' displays '77' as expected.
I then set address '2000' to 'CC'
I go to address '0000' and verify it is 'CC'.  The 2K memory block as mapped to the first K.

I repeat the process on the PAL-2
Set the dip switches to the 'fully-loaded' configuration as specified on the board silk screen

I set memory addres '0000' to '77'

I set memory address '2000' to 'AA'

I flip all DIP switches (0-7) to the OFF position.
The value displayed at address '2000' does not change.
However, it becomes read-only.  If I press 'DA' and try to enter a new value, it does not change.

Flipping switches 1-7 (leaving switch 0 off), and it becomes writable again.

Is this a difference in PAL-2 vs PAL-1 or do I have something amiss with mine?

[GN Liu]

Those are the correct behaviors for both PAL-1 and PAL-2. The difference lies in their onboard decoding and the RAM chip.

[Jeremy Starcher]

Thank you for confirming that is the expected behavior