Interrupt Controller (8259A)
ICW2
The second Initialization Control Word (ICW2), also required in all
modes of operation, is located at I/O address 21h. It consists of the
following:
a)
For programming as a master PIC with slaves on all inputs,
write 00h in ICW2. Although in this case ICW2 conveys no
information, it is required to prepare the master PIC for either
ICW3 or ICW4 (or both) to follow.
b)
For programming as a master with slaves on some inputs, write
ICW2 to establish the base vector address table in memory. Bits
D0-D7 specify the interrupt type desired (0-255) and must be
defined as a multiple of 8, for the eight interrupts in the PIC.
Hence D0-D2 are always 0 for ICW2. The memory address of
the vector table is obtained by multiplying the type by 4. For
example, to use the last eight vector types (248-255), program
bits D3-D7 with 11111B. The three least significant bits of the
vector determine which unique vector in the range 248-255 is
selected and are set by the PIC.
ICW3
The third Initialization Control Word (ICW3) is required only if
bit 1 = 0 in ICW1, denoting that multiple PICs are used; that is, one or
more PICs are slaves to the on-board master PIC. It is located at I/O
address 21h. The S0-S7 bits correspond to the IR0-IR7 bits of the
master PIC. For example, if a slave PIC is connected to the master
PIC IR3 input, code bit 3 = 1.
12-14
Содержание ZT 8809A
Страница 15: ...Tables Table B 9 J5 Pin Assignments B 17 Table B 10 J6 Pin Assignments B 18 Table B 11 J7 Pin Assignments B 19...
Страница 334: ...Jumper Configurations W49 W48 A W47 B A B W37 W66 A W50 B C J7 W67 Figure A 11 W37 W47 50 W66 W67 Jumper Blocks A 34...
Страница 346: ...Jumper Configurations W61 W60 W62 W63 W64 A B A B W65 Figure A 13 W60 W65 Jumper Block A 46...