I'm implementing a driver for the Intel 8259A PIC for x86. To do this properly, I am reading the Intel 8259A PIC Datasheet. It is halfway comprehensible even for someone who approaches controller chips exclusively from the software perspective like me but there is this diagram I don't get:
It is the 8-bit pointer sent from the controller to the CPU in response to the second #INTA (interrupt acknowledgement) raise.
IR is an abbreviation for "interrupt request," the
D bits denote the data lines of the 8-bit data buffer of the controller.
What are these
T7? The datasheet does not mention them ever again, they are just there. I already wrote a driver for the Intel 8042 (guided by the IBM 5170 (PC AT) Technical Reference) and the
T1 bits were called "test inputs" there (p. 1-44).
Is that related to the
T bits from the description of the Intel 8042 controller? What other meaning could these names have?