IBM System 360 Model 30 VHDL files

This update: 2010-07-16

This page contains the VHDL source for a 360/30 implementation, plus compiled files suitable for use on a Digilent Spartan 3 board.

The VHDL is a literal translation of the diagrams that can be found in the FMD manual (Bitsavers mirror). Where errors are suspected, these are flagged in the VHDL, typically using "??".

The Model 30 was implemented using transparent latches and SR flip-flops. These are not a good fit for an FPGA, which prefers edge-triggered flip-flops, but as the timing requirements are not onerous it works well. There are some cases where explicit delays have been added to allow the circuitry to work as intended.

The front panel output is via VGA using the 3-bit interface provided on the board. Switch inputs are via multiplexed rotary switches, and the on-board pushbuttons and slide switches. Both the panel and switch sections are in their own files for ease of modification. The switch file contains details of how the switches are wired in. Basically, the 10 hex-encoded switches are scanned via 10 outputs and 4 inputs, and the remaining 8 switch inputs are discrete. The 'PROC' positions are not connected, so disconnecting the entire switch assembly defaults all switches to the 'Process' position.

If anyone ports this to an alternative FPGA board, please let me have the relevant files and I will host them here.