Long time ago I built a LED display and a hex keypad for my COSMICOS. I lend the COSMICOS and the extensions to a friend's brother and I saw the parts never again. Thanks to Lee Hart's 1802 Membership Card I have a 1802 SBC again. Now I need a display and a keypad for this gem.

Hardware

TIL311 hexadecimal displays were to expensive for me 35 years ago and now they are not easy to get (and still expensive). The 4×7 rounded font looks far better than the seven-segment display especially the lower case hex display letters. But there is an alternative: LTP-305 from LITEON. They have no integrated driver, but the matrix LED driver IC IS31FL3730 can drive two of them. And better there is PCB HAT with 6 LTP-305 and 3 IS31FL3730 on it from Pimoroni ready for the Raspberry Pi. Four digits for the address and two digits for data!

TIL311 Hexadecimal Display

LTP-305 Dot Matrix Display

Microdot_pHAT on Raspberry Pi Zero

https://shop.pimoroni.com/products/microdot-phat

Software for the Raspberry Pi

The Raspi controls the display through its I2C interface.

I still want to use the 1802 Membership Card's Front Panel Card. That means I have to use the D-SUB connector. But there is no address bus on this connector, therefor the address is only valid as long as the DMA (load mode) is used. The data bus is not available too, you will see the data in the load mode and the output port during the run mode.

How to get and build the RaspiElf Display Software

Get the source from the GIT repository (if you have not installed GIT yet, then install it with sudo apt-get install git), type only the bold text after the $ sign:

pi@cosmac:~/elf $ git clone https://github.com/spyren/RaspiElf
Cloning into 'RaspiElf'...
remote: Counting objects: 68, done.
remote: Compressing objects: 100% (37/37), done.
remote: Total 68 (delta 32), reused 62 (delta 29), pack-reused 0
Unpacking objects: 100% (68/68), done.
Checking connectivity... done.
pi@cosmac:~/elf $

Build (compile) from the sources:

pi@cosmac:~/elf $ cd RaspiElf
pi@cosmac:~/elf/RaspiElf $ cd display/
pi@cosmac:~/elf/RaspiElf/display $ make
... TBC

Install the binaries into /usr/local/bin

pi@cosmac:~/elf/RaspiElf/display $ sudo make install
... TBC

TIL311 Emulator

The TIL311 has following inputs:

• Data Inputs A, B, C, D
• Latch Input
• Blanking Input
• (Right and Left Decimal)

For 6 digits we need 36 GPIOs. Without blanking 32 GPIOs, shared latch 25 GPIOs. The Raspberry Pi has 26 GPIOs (we can have a latch for the data and a latch for the address).

The Spare Time Gizmo's Elf 2000 display:

• Databus
  • 8 Data Inputs
  • no strobe
• Adressbus
  • 8 Data Inputs
  • 2 Latch Inputs

Only 18 GPIOs needed. Do not forget: the Raspberry Pi GPIOs are not 5 V compatible.