TULIP4041 Startup Question

[MeindertKuipers]

(10-24-2024 04:17 PM)rocket.scientist Wrote:  In the HP-41C/CV/CX Service Manual schematic, the FI line comes straight from the CPU itself. Interestingly my CX keeps FI at about battery voltage even when the calculator is off. It drops to ground only when I remove the battery.

Does this make sense? Can someone with a TULIP measure the voltage for FI right at the module adapter? I'd love to know if this is just a pull-up that is always powered.

Confirmed. FI is high even when the calc is off. Measured on my HP41CX.
In the CPU Detailed Description document it is mentioned that the FI line is pulled high by the CPU when open.