Asante EN/SC teardown

I’m working on a secret project to get a few more 20-year-old computers on the Internet. Why, I don’t know. I’ve always had a fondness for old Macintosh computers from 1984-1993 (the 68k era), and even gotten a few of these awesome machines on the Internet. To do that nowadays, you’re usually looking at a SCSI to Ethernet converter, such as the Asante EN/SC shown above.

This little box plugs into the SCSI port of an old Powerbook (DB25 SCSI versions also exist), and after the installation of a few drivers a mac from 1987 has a 10BT Ethernet port. Very, very useful.

These adapters are relatively rare and regularly fetch $100 on eBay. With all the cool embedded stuff going on today, I figured I’d tear apart my EN/SC to see how it works and how likely my chances are at building something functionally equivalent.

On the top side, from largest to smallest, I can find

  • 20F001N; 10 Base T filter
  • DP83902AVLJ, a single-chip ethernet controller
  • UM62256DM-70L, a 128kB SRAM
  • Am27C256 a 32kB EPROM
  • Two GAL20V8B programmable logic devices
  • GAL16v8B programmable logic device

On the back of the board,

  • 74FCT648 octal transceiver
  • 74HCT393 ripple counter
  • 74FCT373 octal ripple latch
  • and a huge amount of 0402 resistors

Surprisingly, we’re not dealing with technology that is too obsolete; most of these ICs are readily available save for the Ethernet controller but a quick Google shows that could be sourced relatively easily.

Unfortunately, it’s not quite that simple. Those PLDs probably have a security bit set, meaning it’s impossible for me to figure out how they work. Yes, they could be reverse engineered with a logic analyzer and a shitton of time, but there’s an easier solution to making a new SCSI to Ethernet adapter.

If anyone would want to replicate this project, I’d suggest something along the lines of a CLPD or FPGA to analyze the data coming into and out of the EN/SC. The ideal solution would make use of existing Adaptec drivers, and with very powerful ARM and Ethernet chips it’s not impossible to remake this.

As for me, I’m content with just one EN/SC, so someone else has to do the dirty work on this one. It’s possible, just not easy.

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