Tandy 1000 Technical Reference Manual

Tandy 1000
inter
8259A18259A-2/8259A-8
Technical Reference Manual
OPERATION COMMAND WORDS (OCWs)
Alter the Initialization Command Words (ICWs) are pro-
grammed into the 8259A, the chip is ready to accept
Interrupt requests at its input lines. However, during the
8259A operation, a selection of algorithms can com-
mand the 8259A to operate in various modes through
the Operation Command Words (OCWS).
OPERATION CONTROL WORDS (OCWs)
OCWI
AO 07 oe 05 04 03 02 01 DO
8 ~6M5~-M4-M3M2~
OCW2
0
~
SL EOI 0 L2
L1
LO I
OCW3
0
~ESMM
SMM 0
RR~
OPERATION CONTROL WORD 1 (OCW1)
OCW, sets and clears the mask bits in the interrupt
Mask Register (IMR). M
7
-
M
o
represent the eight mask
bits. M =, indicates the channel is masked
(inhibited), M =0 indicates the channel is enabled
OPERATION CONTROL WORD 2 (OCW2)
R, SL, EOI - These three bits control the Rotate and
End of Interrupt modes and combinations of the two. A
char1 of these combinations .can be found on the Opera-
tion Command Word Format.
L
2
,
L
T
,
L
o
- These bits determine the Interrupt level acted
upon when the SL bit is active
OPERATION CONTROL WORD 3 (OCW3)
ESMM - Enable Special Mask Mode. When this bit is
set to , 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 =, and SMM =,
the 8259A will enter Special Mask Mode If ESMM = ,
and SMM = 0 the 8259A will revert to normal mask mode.
When ESMM = 0, SMM has no effect
2-128

Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200