Tandy 1000 HX - 8259 A Interrupt Controller; Initialization Command Words (ICWS); Operation Command Words (OCWS)

• TANDY COMPUTER PRODUCTS
51
NOTE: Peripherals Requesting an interrupt service must
generate a low to high edge and then remain at a
logic high until service is acknowledged. Failure
to do so will result in a Default Service for IRQ7.
0021 8259A Interrupt Controller
INITIALIZATION CONTROL WORD 2
BitO - 7: Not Used
Bit3 - 7: T3 - T7 of Interrupt Vector Address
(8086/8088 Mode)
INITIALIZATION CONTROL WORD 3 (Master Device)
BitO - 7: =1 Indicated IR input has a slave
=0 Indicated IR input does not have
a slave
INITIALIZATION CONTROL WORD 3 (Slave Device)
BitO - 2 = IDO - 2
Bit3 -7=0 (Not Used)
INITIALIZATION CONTROL WORD 4
BitO: Type of Processor
=0 MCS-80/85 Mode
=1 8086/8088 Mode
Bitl: Type of End Of Interrupt
=0 Normal EOI
=1 Auto EOI
Bit2 - 3: Buffering Mode
Bit3 Bit2
0 X Non-buffered Mode
1 0 Buffered Mode/Slave
1 1 Buffered Mode/Master
Bit4: Nesting Mode
=0 Not Special Fully Nested Mode
=1 Special Fully Nested Mode
Bit5 - 7: =0 (Not Used)
OPERATION CONTROL WORD 1 (IOR*/IOW*)
BitO - 7: Interrupt Mask for IRQ0 - IRQ7
=0 Mask Reset (Enable)
=1 Mask Set (Disable)
BitO
0
0
0
0
1
1
1
1
Bitl
0
0
1
1
0
0
1
1
Bit2
0
1
0
1
0
1
0
1
- Slave ID #
0
1
2
3
4
5
6
7