Grappler Minus 2.0: four logic chips become one

The Grappler Minus has been out of stock for a while. We didn't just reorder the old board. We redesigned it, and the new one is running on real hardware now.

If you haven't seen the card before: it sits in an Apple II slot next to your Disk II controller card and adds SmartPort support using Wing Yeung's SoftSP DIY ROM. It works on the II Plus, Europlus, J-Plus, IIe and IIe Platinum. You still need a Disk II controller or a 5.25 Drive Card. That part hasn't changed.

What changed

The name tells you where the design came from. The Grappler Minus is the Grappler Plus circuit with everything removed except the logic this job needs. By V1.6 we had it down to four 74LS chips: a 74LS00, a 74LS279, a 74LS08 and a 74LS30.

In 2.0 those four are gone too. Their logic now lives in one programmable logic chip (a PLD) in a DIP24 package.

The LED driver went the same way. The old board needed a 2N3906 and a resistor to run the activity LED. The PLD drives it directly now, so that transistor is off the board too.

Why bother

Most people buy the Grappler Minus as a kit. Four 14-pin chips mean four chances to put one in the wrong socket or solder it in backwards. One chip is harder to get wrong.

It also means fewer parts to source. 74LS parts are still easy to find today, but we'd rather not depend on four different ones.

Does it work

Yes. The first prototype booted and ran SmartPort with no fixes needed. The LED behaves the same as before: it blinks during SmartPort access and stays off in normal Disk II mode.

About the SoftSP card

With only two chips left on the board, the PLD and the ROM, 2.0 may have ended up looking a lot like the SoftSP card from MFA2 WorkShop. They aren't the same design. Ours reproduces the Grappler Plus logic as it is, just inside a PLD. The SoftSP card is a circuit built from the start to run SoftSP. Both cards have the same purpose and you use them the same way, but the designs are completely different.

If you'd rather have a finished card, the SoftSP card is sold in the US here: https://ct6502.org/product/softsp/

What's next

We're finishing the PCB layout now. The kit will ship with the PLD already programmed, so you won't need a programmer. Price and release date aren't set yet. We'll post here when the boards arrive.

The SoftSP DIY ROM is by Wing Yeung (MFA2 WorkShop) and is used with his permission, same as before.