82C836 Datasheet, PDF (84/205 Pages) List of Unclassifed Manufacturers – Single-Chip 386sx AT

s Programming the Interrupt Controller
Interrupt Controller
Programming the Interrupt Controller
Two types of commands are used to control the 82C836 interrupt controllers:
Initialization Command Words (ICWs) and Operational Command Words (OCWs).
Initialization Command Words
The initialization process consists of writing a sequence of four bytes to each interrupt
controller. The initialization sequence is started by writing the first Initialization
Command Word (ICW1) to address 020H (0A0H) with a one on bit 4 of the data byte.
The interrupt controller interprets this as the start of the initialization sequence and does
the following:
1. The Initialization Command Word Counter is reset to zero.
2. ICW1 is latched into the device.
3. Fixed Priority mode is selected.
4. IR7 is assigned the highest priority.
5. The Interrupt Mask Register is cleared.
6. The Slave mode address is set to seven.
7. Special Mask mode is disabled.
8. The IRR is selected for Status Read operations.
The next three I/Os write to address 021H (0A1H) will load ICW2-ICW4. See Figure
7-3 shown earlier for a flow chart of the initialization sequence. The initialization
sequence can be terminated at any point (all four bytes must be written for the controller
to be properly initialized) by writing to address 020H (0A0H) with a zero in data bit 4.
Note that this causes OCW2 or OCW3 to be written.
7-8 Revision 3.0
PRELIMINARY
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