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HP41 FI data line - Printable Version

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HP41 FI data line - Nate Martin - 02-07-2016 09:20 PM

Should the FI data line go high or low to indicate data available? FI line from the I/O ports?



RE: HP41 FI data line - Diego Diaz - 04-13-2016 09:36 AM

Hi Nate,

In short, no, FI is the Flag Input line.

I'll add that this is the obscurest and most poorly documented line from the I/O interface. :-)

It's used only by peripherals (PRINTER, HP-IL, WAND, etc) when requesting service from the CPU and is held high for a full digit time (four clock bit time cycles). The exact digit when the FI line is high informs the CPU of the type of service/periphera requesting service.

To the best of my knowledge, apart from said peripherals, only the CL CPU (for obvious reasons) and the USB-41 (to simulate 82143A printer) handle this line. It has no use on ROM pacs or any other module.

Cheers from Canary Islands.