HardLabs

C128-u3-replacement

ytmytm·c128-u3-replacement·kicad-c128d/c128-u3-gal.kicad_pcb

C128-u3-replacement PCB layout, top view — open source board by ytmytm

About the C128-u3-replacement PCB

C128-u3-replacement is an open source PCB design by ytmytm, published on GitHub under the MIT license. It is a 2-layer board measuring 21.5 × 37.3 mm, with 5 components from 5 distinct parts.

Other key parts include the 74LS138 and GAL22V10. By type, the board carries 3 connectors and 2 ICs.

It belongs with the retro computing designs in this gallery.

From the project

Replacement for I/O space address decoder (U3 in C128) with extra features

This is a daughterboard that replaces U3 (74LS138) with a GAL22V10 as the I/O space address decoder providing extra features.

I needed it to split the I/O ($D000-$DFFF) space into more parts to support additional devices I had installed in my C128DCR: ACIA, SID#2 and CIA#3.

The daughterboard (bottom left, just above ROMs) mimics U3 that was already on the mainboard and generates additional chip select signals for:

C128-u3-replacement, from the project README
From the project README

Main components on the C128-u3-replacement

74LS138GAL22V10

C128-u3-replacement bill of materials (BOM)

5 components, 5 distinct parts.

QtyPartRefs
1
74LS138
U1
1
GAL22V10
U2
1
Conn_02x04_Row_Letter_Last
J1
1
Conn_01x02
J2
1
Conn_01x04
J3

C128-u3-replacement design files

The KiCad project lives in the ytmytm/c128-u3-replacement repository on GitHub; these links point at the commit this page was built from.

C128-u3-replacement: common questions

How big is the C128-u3-replacement PCB?

The C128-u3-replacement measures 21.5 × 37.3 mm, has 2 copper layers and is 1.6 mm thick.

How many components are on the C128-u3-replacement?

5 components, from 5 distinct parts. The full bill of materials is listed on this page.

Where can I download the C128-u3-replacement design files?

From the ytmytm/c128-u3-replacement repository on GitHub, which has the KiCad layout and the schematic; the links under Design files point to each one.

Can I use the C128-u3-replacement design in my own project?

Yes, under the terms of its MIT license, which ytmytm chose for the repository.

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