Tandy 1000 Technical Reference Manual

Tandy 1000
Technical Reference Manual
inter
8259A18259A-2/8259A-8
INTERRUPT
SEQUENCE OUTPUTS
MCS-80®, MCS-85®
This sequence is timed by three INTA pulses. DUring the
lirst INTA pulse the CALL opcode is enabled onto the
data bus.
Content of First Interrupt
Vector Byte
not issue any data to the processor and leaves its data bus
bulfers disabled. On the second interrupt acknowledge
cycle in iAPX 86 mode the master (or slave if so pro-
grammed) will send a byte 01 data to the processor with
the aCknowledged interrupt code composed as lollows
(note the state of the ADI mode control is .gnored and
A
s
-A11 are unused in iAPX 86 mode):
Content of Third Interrupt
Vector Byte
07 De OS 04 03 02 01 DO
r--A-'S--'-Al-4-'--A-'-J 'I-A-'2-
r
:
-A-'-' ---'--A-'0--'-[' ~
During the third INTA pulse the higher address of the
appropriate service routine, which was programmed as
byte 2 01 the initialization sequence (As - Ad, is
enabled onto the bus
During the second INTA pulse the lower address 01 the
appropriate service routine is enabled onto the data bus
When Interval = 4 bits A
s
-A
7
are programmed, while A
o
-
A~ are automatically inserted by the 8259A. When Inter·
val = 8 only A
6
and A
7
are programmed, while Ao-A
s
are
automatically inserted.
Content of Interrupt Vector Byte
for iAPX 86 System Mode
~-
07
06 05 04
03 02
01
f-0~~
f-----
f-.-
~.
~-
r---
--
IAI
T7 T6 Ts T4 T3
,
. ,
f-
IA6 T7 T6 Ts T4
----
T3
0
lAS T7
T6
Ts T4
T3
IA4
T7 T6 Ts T4
T3
IA3 T7 T6 Ts T4
T3
1-----
~-
IA2
;-!!....+_T~.I
Ts T4 T3
f-----
IA.
T7 I T6
Ts T4
T3
lAO T7
T6
~T4
T3
0
~-
INITIALIZATION COMMAND WORDS
(ICWS)
GENERAL
Whenever a command is issued with AO =0 3nd D4 = 1,
this is interpreted as Initialization Command Word 1
(ICW1). ICW1 starts the Initialization sequence during
which the. follOWing automatically occur
a The edge sense circuit is resel, which means that fol-
lOWing initialization. an interrupt request (IA) Input
must make a low-to-hlgh transition to generate an
Interrupt
b The Interrupt Mask Register is cleared
c IR7 Input IS assigned priority 7
d The slave mode address IS set to 7
e. Special Mask Mode is cleared and Status Read IS set to
IRR
I IIIC4~O. then all functions selected in ICW4 are set to
zero (Non-Buffered mode'. no Auto-EO!. MCS-80. 85
system)
-Not.: Mister/Slave In lew. IS only used In the bullered mode
PROGRAMMING THE 8259A
The 8259A accepts two types 01 command words gener·
ated by the CPU
1 Inllia/izallon Command Words (lCWs,': Belore normal
operation can begin, each 8259A in the system must
be brought to a starting pOint - by a sequence 012 to
4 bytes t.med by WA pulses
2 Operation Command Words IOCWs). These are the
command words which command the 8259A looper·
ate in various Interrupt modes These modes are:
a. Fully nested mode
b, Aotatlng priority mode
c. Special mask mode
d. Polled mode
The OCWs can be written into the 8259A anytime alter
initialization
07 De OS 04 03 02 DIDO
L-,- m~ __ O ~_o _~_---, __ o __ -,--l
Content of Second Interrupt
Vector Byte
IA
Int.",.1-4 . __ ~_~
07
De
OS 04 03 02 01 DO
--- ------- -
A6 AS
1'~ 1 _0 OJ
6
AT A6 AS
1 , 0 0 0
S
107
A6 AS
1 0 , 0 0
4_
A6
AS 1
0 0
0 0
I
AT A6 AS
I
A6 AS
A7
A6 AS
-..0
A6 AS
IA
-~- --- In'.';;I--=a~-l
07
06
OS --0-4 -----03--0-2--01 DO
A6
1 1 1 a 0 a
Al A6 1 1 0 0 0 0
A6
o 0 0
Al A6
o 0
A6
n 0
A6
o ~ I
A6
Al
A6
CALL CODE
iAPX 86, iAPX 88
iAPX 86 mode IS similar to MCS-80 mode except that only
two Interrupt Acknowledge cycles are Issued by the pro-
cessor and no CALL opcode IS sent to the processor. The
first Interrupt acknowledge cycle IS Similar to that 01
MCS-80, 85 systems in that the 8259A uses It to IOternally
freeze the state of the interrupts for Priority resolution and
as a master it issues the Interrupt code on the cascade
lines at the end 01 the INTA pulse. On this first cycle It does
2-125

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