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Amiga 2000 board in EATX form factor

Published 26.04.2021 - 16:40 by osz

Amiga 2000 board in EATX form factor

This project is currently still a proof-of-concept of a 4-layer open source Amiga 2000 board in EATX format. EATX is simply a larger or extended ATX variant, with a size of 305 × 330 mm. According to the author, this is the better choice for replicating an Amiga 2000 board, given the length of the Zorro II cards and the abundance of components for the Amiga 2000. Proof-of-concept means that there may still be errors in the circuit diagrams. The board cannot function theoretically or at least not reliably at this point in time. The work on the board is still ongoing.

In contrast to other 1:1 replicas, several things have been changed here in addition to the changed form factor. For example, where necessary, new connector options are beeing used, as some connectors for the Amiga are known to be difficult or impossible to obtain and often have to be soldered from an existing boards in order to reuse them.

Compared to the original Amiga 2000 board, the DB23 video connection was replaced by an HD15 connection (VGA). HSYNC and VSYNC signals are delivered via VGA. As a result, every monitor can be connected and used connecting a standard VGA cable that can cope with the 15 kHz standard. Alternatively, corresponding VGA converters can also be used for other monitors.

In terms of memory, the four 256k DRAM chips have been replaced by an SRAM chip. In addition, an 8372A-Agnus is required, as the board has been configured to recognize 1 MB Chip RAM. Other Agnus revisions are not supported currently.

For the audio output the two chinch connections have been removed and instead a 3.5 mm stereo audio socket is used.

With regard to the power supply unit, the original Amiga 2000 power supply unit is not supported. ATX power supply units with 24-pin connectors are supported instead. It should be noted that -5V is supplied via a voltage regulator located on the board. A reset can be triggered out as usual via Ctrl + L-Amiga + R-Amiga or via the reset switch on the ATX housing.

A lot has happened with the interfaces as well. The number of 16-bit ISA slots has been reduced to three to create additional space on the board. The support for ISA cards via a bridge board is unchanged compared to the original Amiga 2000. Otherwise the internal serial interface has been removed, but the external serial interface has been retained. The external hard disk connector has also been removed. Internally, however, up to two Amiga-compatible hard drives with double density can be connected.

The real-time clock (RTC) was changed to the RTC-62423 chip because it is more precise and relatively readily available.

The 27C400 EPROM is taken into account as the Kickstart ROM currently, as it is relatively easy to obtain. It is also possible to use an original Commodore Kickstart ROM.

Further and more detailed informations and KiCAD files are available in the project's GitHub repository: https://github.com/jasonsbeer/Amiga-2000-ATX
News Source: https://github.com/jasonsbeer/Amiga-2000-ATX

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