NorthStar Horizon Monitor
The NorthStar Z80 CPU board allows for 1K of firmware to be installed on a 2708 EPROM
This was an optional extra and they provided an monitor program called HDT. Although I have the upgrade the EPROM is corrupt and have not found a copy of the software on the Internet so decided to write my own.
I have blank 2708's its an early device that requires three voltages, a special programmer and some additions to the board. Plus it uses more power than modern chips. So I decided to replace it with a modern EEPROM
I found a website with a home made adaptor, and decided to design a PCB.
- Pin 21 /W is connected to pin 24 VCC.
This ensures it is not connected to the -5V supplied by the 2708 socket and ensures the chip will only be read.
- Pin 19 A10 is connected to pin 12 VSS.
This ensures it is not connected to the +12V supplied by the 2708 socket and allows only the first 1K of the 28C16 to be read by forcing A10 to always be 0.
- Pin 18 /E is connected to pin 12 VSS.
This ensures the 28C16 is always enabled with pin 20 /G latching data on pins DQ0-DQ7. The 28C16 is low power compared to the 2708 so having the chip always enabled is OK.
I can read some test code from the EEPROM on my NorthStar so next step is to decide what functions are needed, and to write and test some code.
I have PCB's available