16K Memory Board is Complete

The 16K memory board is assembled and works fine.  It has two sockets for 8K RAM, EPROM, or EEPROM chips, so you can add any combination of 16K RAM, 16K EPROM/EEPROM, or 8K RAM and 8K EPROM/EEPROM. The EEPROM is writeable but needs to be written with a delay after each write (approximately 1ms depending on the brand of chip used). There are jumpers for each chip to enable writing, so that the EEPROMs can be made read-only, if desired.

Memory Board Installed in Replica 1

I ran the memory test in my JMON monitor on the board stuffed with RAM to verify it.

Running Memory Test on 16K RAM 

So, for example, I could put Applesoft Lite or Enhanced BASIC in ROM (these are too big for the one 8K EEPROM on the Replica 1), or I could use RAM and bring the Replica 1 up to 48KB of contiguous RAM, twelve times what the original Apple 1 had (and then run really big programs).

I only used about half the protoboard, so I could add more circuitry to it later.

Wiring Side of Memory Board

I've put the design files here in case anyone wants to build their own or adapt the design for their own projects.

16K Memory Card Progress

I've now wired up most of the memory board for the Replica 1. I started with the address decoding and control lines and confirmed that it worked (e.g reading addresses in the correct range generated appropriate chip select signals as observed on an oscilloscope).

Testing Address Decoding

I then wired up the first of the two EEPROM/RAM sockets and confirmed that it is working, both with EEPROM and RAM chips. I now need to wire up the second memory chip socket.

Component Side

The wiring is rather tedious and time consuming. I might consider wirewrap for future projects, although the end result doesn't look as attractive with the big wirewrap pins sticking out of the back of the board.

Wiring Side

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I'm also continuing to tweak the Apple 1 BASIC source, adding comments.