4-9
The address format is 2 bytes long (A0 - A15). When the
routine interval is 4, A0 - A4 are automatically inserted by
the 82C59A, while A5 - A15 are programmed externally.
When the routine interval is 8, A0 - A5 are automatically
inserted by the 82C59A while A6 - A15 are programmed
externally.
The 8-byte interval will maintain compatibility with current
software, while the 4-byte interval is best for a compact jump
table.
In an 80C86/88/286 system, A15 - A11 are inserted in the
five most significant bits of the vectoring byte and the
82C59A sets the three least significant bits according to the
interrupt level. A10 - A5 are ignored and ADI (Address inter-
val) has no effect.
LTlM: If LTlM = 1, then the 82C59A will operate in the level
interrupt mode. Edge detect logic on the interrupt
inputs will be disabled.
ADI: ALL address interval. ADI = 1 then interval = 4; ADI
= 0 then interval = 8.
SNGL: Single. Means that this is the only 82C59A in the
system. If SNGL = 1, no ICW3 will be issued.
IC4: If this bit is set - lCW4 has to be issued. If lCW4 is
not needed, set lC4 = 0.
Initialization Command Word 3 (ICW3)
This word is read only when there is more than one 82C59A
in the system and cascading is used, in which case
SNGL = 0. It will load the 8-bit slave register. The functions of
this register are:
a. In the master mode (either when
SP = 1, or in buffered
mode when M/S = 1 in lCW4) a “1” is set for each slave in
the bit corresponding to the appropriate IR line for the
slave. The master then will release byte 1 of the call
sequence (for 8080/85 system) and will enable the corre-
sponding slave to release bytes 2 and 3 (for 80C86/88/
286, only byte 2) through the cascade lines.
b. In the slave mode (either when
SP = 0, or if BUF = 1 and
M/S = 0 in lCW4), bits 2 - 0 identify the slave. The slave
compares its cascade input with these bits and if they are
equal, bytes 2 and 3 of the call sequence (or just byte 2 for
80C86/88/286) are released by it on the Data Bus.
NOTE: (The slave address must correspond to the IR line it is con-
nected to in the master ID).
Initialization Command Word 4 (ICW4)
SFNM: If SFNM = 1, the special fully nested mode is pro-
grammed.
BUF: If BUF = 1, the buffered mode is programmed. In
buffered mode,
SP/EN becomes an enable output
and the master/slave determination is by M/S.
M/S: If buffered mode is selected: M/S = 1 means the
82C59A is programmed to be a master, M/S = 0
means the 82C59A is programmed to be a slave. If
BUF = 0, M/S has no function.
AEOI: If AEOI = 1, the automatic end of interrupt mode is
programmed.
µPM: Microprocessor mode: µPM = 0 sets the 82C59A for
8080/85 system operation, µPM = 1 sets the
82C59A for 80C86/88/286 system operation.
Operation Command Words (OCWs)
After the Initialization Command Words (lCWs) are pro-
grammed into the 82C59A, the device is ready to accept
interrupt requests at its input lines. However, during the
82C59A operation, a selection of algorithms can command
the 82C59A to operate in various modes through the Opera-
tion Command Words (OCWs).
Operation Command Word 1 (OCW1)
OCW1 sets and clears the mask bits in the Interrupt Mask
Register (lMR) M7 - M0 represent the eight mask bits. M = 1
indicates the channel is masked (inhibited), M = 0 indicates
the channel is enabled.
Operation Command Word 2 (OCW2)
R, SL, EOI - These three bits control the Rotate and End of
Interrupt modes and combinations of the two. A chart of
these combinations can be found on the Operation Com-
mand Word Format.
L2, L1, L0 - These bits determine the interrupt level acted
upon when the SL bit is active.
Operation Command Word 3 (OCW3)
ESMM - Enable Special Mask Mode. When this bit is set to 1
it enables the SMM bit to set or reset the Special Mask
Mode. When ESMM = 0, the SMM bit becomes a “don’t
care”.
SMM - Special Mask Mode. If ESMM = 1 and SMM = 1, the
82C59A will enter Special Mask Mode. If ESMM = 1 and
SMM = 0, the 82C59A will revert to normal mask mode.
When ESMM = 0, SMM has no effect.
Fully Nested Mode
This mode is entered after initialization unless another mode
is programmed. The interrupt requests are ordered in priority
from 0 through 7 (0 highest). When an interrupt is acknowl-
edged the highest priority request is determined and its vec-
tor placed on the bus. Additionally, a bit of the Interrupt
Service register (IS0 - 7) is set. This bit remains set until the
microprocessor issues an End of Interrupt (EOI) command
OPERATION COMMAND WORDS (OCWs)
A0 D7 D6 D5 D4 D3 D2 D1 D0
OCW1
1 M7M6M5M4M3M2M1M0
OCW2
0 R SL EOI 0 0 L2 L1 L0
OCW3
0 0 ESMM SMM 0 1 P RR RIS
82C59A
