----------P0020003F--------------------------
PORT 0020-003F - PIC 1 - PROGRAMMABLE INTERRUPT CONTROLLER (8259A)
SeeAlso: PORT 00A0h-00AFh"PIC 2",INT 08"IRQ0",INT 0F"IRQ7"

0020  -W  PIC initialization command word ICW1 (see #P0010)
0020  -W  PIC output control word OCW2 (see #P0015)
0020  -W  PIC output control word OCW3 (see #P0016)
0020  R-  PIC  interrupt request/in-service registers after OCW3
		request register:
		 bit 7-0 = 0  no active request for the corresponding int. line
			 = 1  active request for corresponding interrupt line
		in-service register:
		 bit 7-0 = 0  corresponding line not currently being serviced
			 = 1  corresponding int. line currently being serviced

0021  -W  PIC ICW2,ICW3,ICW4 immed after ICW1 to 0020 (see #P0011,#P0012,#P0013)
0021  RW  PIC master interrupt mask register OCW1 (see #P0014)

Bitfields for PIC initialization command word ICW1:
Bit(s)	Description	(Table P0010)
 7-5	0 (only used in 8080/8085 mode)
 4	ICW1 is being issued
 3	(LTIM)
	=0  edge triggered mode
	=1  level triggered mode
 2	interrupt vector size
	=0 successive interrupt vectors use 8 bytes (8080/8085)
	=1 successive interrupt vectors use 4 bytes (80x86)
 1	(SNGL)
	=0  cascade mode
	=1  single mode, no ICW3 needed
 0	ICW4 needed
SeeAlso: #P0011,#P0012,#P0013

Bitfields for PIC initialization command word ICW2:
Bit(s)	Description	(Table P0011)
 7-3	address lines A0-A3 of base vector address for PIC
 2-0	reserved
SeeAlso: #P0010,#P0012,#P0013

Bitfields for PIC initialization command word ICW3:
Bit(s)	Description	(Table P0012)
 7-0	=0 slave controller not attached to corresponding interrupt pin
	=1 slave controller attached to corresponding interrupt pin
SeeAlso: #P0010,#P0011,#P0013

Bitfields for PIC initialization command word ICW4:
Bit(s)	Description	(Table P0013)
 7-5	reserved (0)
 4	running in special fully-nested mode
 3-2	mode
	0x nonbuffered mode
	10 buffered mode/slave
	11 buffered mode/master
 1	Auto EOI
 0	=0  8085 mode
	=1  8086/8088 mode
SeeAlso: #P0010,#P0011,#P0012

Bitfields for PIC output control word OCW1:
Bit(s)	Description	(Table P0014)
 7	disable IRQ7 (parallel printer interrupt)
 6	disable IRQ6 (diskette interrupt)
 5	disable IRQ5 (fixed disk interrupt)
 4	disable IRQ4 (serial port 1 interrupt)
 3	disable IRQ3 (serial port 2 interrupt)
 2	disable IRQ2 (video interrupt)
 1	disable IRQ1 (keyboard, mouse, RTC interrupt)
 0	disable IRQ0 (timer interrupt)
SeeAlso: #P0015,#P0016,#P0418

Bitfields for PIC output control word OCW2:
Bit(s)	Description	(Table P0015)
 7-5	operation
	000 rotate in auto EOI mode (clear)
	001 (WORD_A) nonspecific EOI
	010 (WORD_H) no operation
	011 (WORD_B) specific EOI
	100 (WORD_F) rotate in auto EOI mode (set)
	101 (WORD_C) rotate on nonspecific EOI command
	110 (WORD_E) set priority command
	111 (WORD_D) rotate on specific EOI command
 4-3	reserved (00 - signals OCW2)
 2-0	interrupt request to which the command applies
	(only used by WORD_B, WORD_D, and WORD_E)
SeeAlso: #P0014,#P0016

Bitfields for PIC output control word OCW3:
Bit(s)	Description	(Table P0016)
 7	reserved (0)
 6-5	special mask
	0x  no operation
	10  reset special mask
	11  set special mask mode
 4-3	reserved (01 - signals OCW3)
 2	poll command
 1-0	function
	0x  no operation
	10  read interrupt request register on next read from PORT 0020h
	11  read interrupt in-service register on next read from PORT 0020h
Note:	the special mask mode permits all other interrupts (even those with
	  lower priority) to be processed while an interrupt is already in
	  service, but will not re-issue an interrupt for a particular IRQ
	  while it remains in service
SeeAlso: #P0014,#P0015
----------P00A000AF--------------------------
PORT 00A0-00AF - PIC 2 - PROGRAMMABLE INTERRUPT CONTROLLER (8259A)
SeeAlso: PORT 0020h-003Fh"PIC 1",INT 70"IRQ8",INT 77"IRQ15"

00A0  RW  PIC 2	 same as 0020 for PIC 1
00A1  RW  PIC 2	 same as 0021 for PIC 1 except for OCW1 (see #P0418)

Bitfields for PIC2 output control word OCW1:
Bit(s)	Description	(Table P0418)
 7	disable IRQ15 (reserved)
 6	disable IRQ14 (fixed disk interrupt)
 5	disable IRQ13 (coprocessor exception interrupt)
 4	disable IRQ12 (mouse interrupt)
 3	disable IRQ11 (reserved)
 2	disable IRQ10 (reserved)
 1	disable IRQ9  (redirect cascade)
 0	disable IRQ8  (real-time clock interrupt)
SeeAlso: #P0014
----------P00A0------------------------------
PORT 00A0 - XT - NMI MASK REGISTER
SeeAlso: PORT 0070h,INT 02

00A0  RW  NMI mask register (XT only)
	 bit 7 = 0 NMI signal disabled from reaching CPU
	       = 1 NMI signal enabled
