HS-82C55ARH
TABLE 3.
A1
X
A0
X
RD
1
WR
1
CS
0
DISABLE FUNCTION
Data Bus - 3-State
Mode 0 to monitor simple switch closings or display
computational results, Group A could be programmed in
Mode 1 to monitor a keyboard or tape recorder on an
interrupt-driven basis.
The mode definitions and possible mode combinations may
seem confusing at first but after a cursory review of the
complete device operation a simple, logical I/O approach will
surface. The design of the HS-82C55ARH has taken into
account things such as efficient PC board layout, control
signal definition vs PC layout and complete functional
flexibility to support almost any peripheral device with no
external logic. Such design represents the maximum use of
the available pins.
CONTROL WORD
D7 D6 D5 D4 D3 D2 D1 D0
BIT SET/RESET
X
X
X
1 = SET
0 = RESET
BIT SELECT
0
0
0
0
1
1
0
0
2
0
1
0
3
1
1
0
4
0
0
1
5
1
0
1
6
0
1
1
7
1 B0
1 B1
1 B2
CONTROL WORD
D7 D6 D5 D4 D3 D2 D1 D0
GROUP B
PORT C (LOWER)
1 = INPUT
0 = OUTPUT
PORT B
1 = INPUT
0 = OUTPUT
MODE SELECTION
0 = MODE 0
1 = MODE 1
GROUP A
PORT C (UPPER)
1 = INPUT
0 = OUTPUT
PORT A
1 = INPUT
0 = OUTPUT
MODE SELECTION
00 = MODE 0
01 = MODE 1
1X = MODE 2
DON’T
CARE
MODE SET FLAG
1 = ACTIVE
BIT SET/RESET FLAG
0 = ACTIVE
FIGURE 11. MODE SET CONTROL WORD FORMAT
Mode Selection
There are three basic modes of operation that can be
selected by the system software:
Mode 0 - Basic Input/Output
Mode 1 - Strobed Input/Output
Mode 2 - Bidirectional Bus
When the RESET input goes “high”, all ports will be set to
the input mode with all 24 port lines held at the logic “one”
level by internal bus hold devices. After reset, the
HS-82C55ARH can remain in the input mode with no
additional initialization required. This eliminates the need for
pull-up or pull-down resistors in all CMOS designs. During
the execution of the system program, any of the other modes
may be selected using a single output instruction. This
allows a single HS-82C55ARH to service a variety of
peripheral devices with a simple software maintenance
routine.
The modes for Port A and Port B can be separately defined
while Port C is divided into two portions as required by the
Port A and Port B definitions. All of the output registers,
including the status register, will be reset whenever the
mode is changed. Modes may be combined so that their
functional definition can be “tailored” to almost any I/O
structure. For instance: Group B can be programmed in
FIGURE 12. BIT SET/RESET CONTROL WORD FORMAT
Single Bit/Set/Reset Feature
Any of the eight bits of Port C can be Set or Reset using a
single OUTput instruction. See Figure 12. This feature
reduces software requirements in control-based
applications.
Interrupt Control Functions
When the HS-82C55ARH is programmed to operate in Mode
1 or Mode 2, control signals are provided that can be used
as interrupt request inputs to the CPU. The interrupt request
signals, generated from Port C, can be inhibited or enable by
setting or resetting the associated INTE flip-flop, using the
Bit Set/Reset function of Port C.
This function allows the programmer to enable or disable a
CPU interrupt by a specific I/O device without affecting any
other device in the interrupt structure.
INTE Flip-Flop Definition:
(BIT-SET) - INTE is SET - Interrupt enable.
(BIT-RESET) - INTE is RESET - Interrupt disable.
NOTE: All mask flip-flops are automatically reset during mode
selection and device Reset.
8
INTERSIL [ INTERSIL CORPORATION ]
