# TK2000 BUS EXTENDER

## DISCLAIMER

Any use of this project is **under your own responsibility**.
You will be responsible of checking the correct construction and functionality of your board.
By using this project You will agree that I cannot be held responsible if it will destroy any of your devices, damage your computer, burn down your house or whatever.

## Introduction

This board is a bus extender for the TK2000 computer, and allows plugging in up to 3 expansion boards into it.

Differently from what happens in the Apple II, the TK2000 does not differentiate between the expansion slots: every connector brings out the same signals, and it's up
to the boards installed in there to decode the signals appropriately and decide which memory/IO range to use.

![Empty adapter connected to a TK2000 clone](pics/adapter_empty.jpg)

![Adapter with two installed boards](pics/adapter_with_boards.jpg)


## Hardware

The board was designed with [KiCad](https://kicad.org/) EDA.

### Bill of Materials

| Component              | Qty | Type / Value                                            | Notes                                                                |
| ---------------------- | --- | ------------------------------------------------------- | -------------------------------------------------------------------- |
| P2, P3, P4             |  3  | 50 pin (2x25) female edge connector, 2.54mm pitch       | https://aliexpress.com/item/1005008354411366.html                    |
| P7                     |  1  | 50 pin (2x25) pin header                                | Optional, debug only                                                 |
| C1 - C6                |  6  | 10uF/25V+ 1206 MLCC capacitors                          |                                                                      |
| F1                     |  1  | 1.5A 1812 fuse                                          |                                                                      |
| F2, F4                 |  2  | 0.5A 1206 fuse                                          |                                                                      |
| F3                     |  1  | 0.25A 1206 fuse                                         |                                                                      |
| C7                     |  1  | 100pF/16V+ 0805 MLCC capacitor                          | Optional, introduces a delay in Φ2 signal, improves compatibility with some cards |

Bridge JP1, JP2, JP3 and JP4 to connect the DMA and IRQ passthrough chains.

### Ordering the boards

You can order the board for this project at [PCBWay](https://www.pcbway.com/project/shareproject/TK2000_Bus_extender_794f587e.html) and support me or download 
the gerbers and have them printed wherever you like!!!

### Fixes

#### Rev. 1 and 2

Adding a small 100pF capacitor between Φ2 and GND improves compatibility with 65C22 cards that seemed very sensitive to the speed and type of glue logic used to interface them with the bus.

Rev. 3 has a footprint to install this option capacitor, previous revisions require a mod, where the ground trace is scratched to expose the copper and the cap is soldered to the pin on the underside.

![Modified phi2 circuit with capacitor soldered under the board](pics/cap_mod_phi2.jpg)