DDL4-CPU

I am using some right angle male and female connectors to interface each of the modules. When the headers are at least 150mils (3.80mm) from the edge of the board, they "self-align" with the surface of the PCB. Unfortunately the connector to the Clock Generator Module on the PC-IR Module, was only 75mils from the edge, so it would not self align to the PCB. I went ahead and soldered the matching connector on the Clock Generator Module, and used my Hackaday Stick-Vise to align the two PCBs and soldered the header in place. This has been added to the "fix list" for revision B!

Two modules assembled... six to go! The Decode Module was the next easiest one to assemble, so I figured I would complete it this evening. It uses the same Low Insertion Force (LIF) sockets as on the ROM Module, as well as the same Atmel 8k x 8 eeprom. Using the 8k x 8 eeprom is extreme overkill for the decode module, however, since I was already purchasing some of the Atmel eeproms, I could use them for the Decode Module as well. I think in future versions I might go with a smaller eeprom, or even a small CPLD. This module consists of the two eeproms, a 74LVC193 4-bit counter tied to a 74LVC138 1-of-8 decoder. These two combine to control each of the 7 phases of the microprogramming. I've added LEDs to indicate the phase state as well as some LEDs to display the primary clock status. This module connects to 4 other modules, more than any other, so I decided to use female headers on all four sides.

So all of the PCBs arrived yesterday, and all of the remaining parts arrived today.... time to begin assembly. When I started looking at the boards this evening, my original intention was to assemble the boards in a strict order with a log post for each, however, I succumbed to temptation and started with the simplest board: The ROM Module. The ROM Module only consists of three capacitors, the i/o header, and the ROM, so it was the lowest hanging fruit of the design. My intention was to populate the board with a standard socket, and then use a Zero Insertion Force (ZIF) socket on top of that, but after visiting my local surplus shop Tanner Electronics, I discovered they had some inexpensive Low Insertion Force (LIF) sockets. The price was right and they seemed to do the job, so I purchased 10 pieces. I will also be using these LIF sockets on the Decode Module. I've selected the Atmel AT28C64B-15SU EEPROM to use in this project. It's an 8k x 8 device, supported by most of the inexpensive eeprom programmers like the TL866 series which we will discuss in a later log post. In addition, they are relatively inexpensive, and available in quantity from retailers like Digikey and Mouser. One down... seven to go..