Prototypes for the new AppleIISd hardware V1.2
A couple of days ago, the prototypes for the new hardware version 1.2 of the AppleIISd arrived. As you may tell, I made a few changes from the original design: the CPLD and the EEPROM are now SMD components, the programming connector for the CPLD is a component-less Tag-Connect, the 3.3V converter was changed and the pullup resistors are now an array. I am quite happy with the design, but I will have to change a few things for the final version, but that is what prototypes are for!
The pin header for CPLD programming will be reintroduced but not equipped next to the Tag-Connect, necessary adapters are not really cheap. The slot connector will have longer pads. The third thing I still have to figure out is the following: about every tenth time the machine is switched on, the first byte of the EEPROM gets erased and I still have not quite figured out why. I am not sure if this happens on power-up or power-down. Adding pullups on the /OE and /WE lines helped to reduce the error to about every 40th time, but that still is too much. Strangely, my retrofitted V1.1 cards do not show this behaviour.
Monitoring the signals on an oscilloscope did not show anything peculiar, yet. CH1 is the 5V supply for the EEPROM, CH2 is the /WE line on a power-down/power-up cycle.
I will have to look further for the needle in the haystack, but I am sure I will have a very convenient product once it is finished.