Reorganization of signals to improve cabling signal integrity

RIBBON CABLE LINKING DE10-NANO, LCD MODULE AND MY 1130 INTERFACE BOARD

The DE10-Nano general purpose IO connectors are 2.54mm 2 x 20 connectors, very like PC disk and floppy connectors, using ribbon cable to carry signals between the ends. I will use the ribbon cables to bring the signals over to the other two boards but they will not work plugging in an identical connector so I have some wiring to accomplish. 

The LCD Module end does not use the same connector, instead it has a space designed to fit a Raspberry Pi Pico. That is similar to a Dual Inline Package but they separated the two rows of 20 pins by an additional 2.54mm thus incompatible with a DIP socket. 

My interface board does use the same 2.54mm 2 x 20 connector however my pin assignments vary. I also use the cable to carry some voltages which I don't want to connect to the DE10-Nano. This means I will be modifying the connections from the cable slightly. Same basic order of the signals, just a few places where the cable is split to skip over pins or slightly realign. 

KiCAD view of the board design

GROUND BETWEEN EACH SIGNAL WIRE TO REDUCE COUPLING

The goal is to minimize signals coupling (being induced in adjacent wires). With ribbon cables it is common to have a ground wire between each signal wire to accomplish this. I thus reassigned the signals on the DE10-Nano connector to allow the signals to be sandwiched between grounds. 

DIVISION OF 1130 ORIENTED AND LCD MODULE ORIENTED SIGNALS BY CONNECTOR

I have signals that connect this product to the IBM 1130 disk drive. Other wires are hooked to the LCD Module to support the user interface with an LCD panel and a touch screen atop it. For simplicity of cabling and routing of wires, I separated these to their own cables. The DE10-Nano has two GPIO connectors, thus I used GPIO 0 for the 1130 related signals and GPIO 1 for the LCD Module wiring. 

MODIFICATION OF WIRING OF MY 1130 INTERFACE BOARD 

My earlier approach to building this product used an Arduino Mega with an LCD daughter card for the user interface and the SD Card where the virtual card images resided, communicating via SPI to a Xilinx S7 based FPGA board, but the toolchain was causing me major grief. That was when I changed horses to the Altera/Intel based DE10-Nano and its more stable toolchain. 

However, the Arduino Mega 2560 board used 5V signaling levels, while the FPGA board was based on 3.3V levels and the IBM 1130 system's SLT is a 3V scheme. To convert voltage levels for signals passing between the boards I developed that interface board which handled 3V, 3.3V and 5V signals. For example, a signal between Arduino and FPGA would convert 5V to 3.3V or vice versa. 

My DE10-Nano and the LCD Module are all based on 3.3V, which changes the voltage levels involved in certain signals. I looked over my board design and schematic and came to the realization that my only change is to connect the power pin for 5V to the 3.3V source, which would cause all the converters to properly shift levels between 3V and 3.3V as needed. 

ADDITIONAL DE10-NANO AND LCD MODULES ORDERED

I expect to build and install a few more of the Virtual 2315 Cartridge Facility products on other IBM 1130 systems. Currently another museum is planning to have me restore their 1130 to operation and its usability will be greatly enhanced by adding one of these to it. The National Museum of Computing in the UK has a running IBM 1130 which could make use of one of these as well.

I picked up another DE10-Nano and some LCD Modules so that I have the key components to build more of these systems.