10
FN6140.1
June 28, 2005
ACK
- (Acknowledge Input). A “l(fā)ow” on this input informs the
82C55A that the data from Port A or Port B is ready to be
accepted. In essence, a response from the peripheral device
indicating that it is ready to accept data, (See Note 1).
INTR
- (Interrupt Request). A “high” on this output can be
used to interrupt the CPU when an output device has
accepted data transmitted by the CPU. INTR is set when
ACK is a “one”, OBF is a “one” and INTE is a “one”. It is reset
by the falling edge of WR.
INTE A
Controlled by Bit Set/Reset of PC6.
INTE B
Controlled by Bit Set/Reset of PC2.
NOTE:
1. To strobe data into the peripheral device, the user must operate
the strobe line in a hand shaking mode. The user needs to send
OBF to the peripheral device, generates an ACK from the
peripheral device and then latch data into the peripheral device
on the rising edge of OBF.
FIGURE 8. MODE 1 OUTPUT
1
D7
0
D6
1
D5
1
D4
1/0
D3 D2 D1 D0
CONTROL WORD
MODE 1 (PORT A)
PC7
8
ACKA
PC6
PA7-PA0
OBFA
INTRA
PC3
PC4, PC5
2
WR
PC4, PC5
1 = INPUT
0 = OUTPUT
1
D7 D6 D5 D4 D3 D2 D1 D0
CONTROL WORD
MODE 1 (PORT B)
PC1
8
ACKB
PC2
INTE
B
PB7-PB0
OBFB
INTRB
PC0
WR
1
0
INTE
A
FIGURE 9. MODE 1 (STROBED OUTPUT)
tWOB
tWB
tAK
tAIT
tAOB
tWIT
OBF
WR
INTR
ACK
OUTPUT
Combinations of Mode 1: Port A and Port B can be individually defined as input or output in Mode 1 to support a wide variety of strobed I/O applications.
FIGURE 10. COMBINATIONS OF MODE 1
1
D7
0
D6
1
D5
1
D4
1/0
D3 D2 D1 D0
CONTROL WORD
PORT A - (STROBED INPUT)
PORT B - (STROBED OUTPUT)
PC4
8
OBFB
PA7-PA0
STBA
INTRB
PC0
PC6, PC7
2
WR
PC6, PC7
1 = INPUT
0 = OUTPUT
8
IIBFA
PC5
INTRA
PC3
ACKB
PC2
I/O
PC1
PB7, PB0
RD
1
0
1
D7
0
D6
1
D5
0
D4
1/0
D3 D2 D1 D0
CONTROL WORD
PORT A - (STROBED OUTPUT)
PORT B - (STROBED INPUT)
PC7
8
STBB
PA7-PA0
OBFA
INTRB
PC0
PC4, PC5
2
RD
PC4, PC5
1 = INPUT
0 = OUTPUT
8
ACKA
PC6
INTRA
PC3
IBFB
PC1
I/O
PC2
PB7, PB0
WR
1
1
MS82C55A, MQ82C55A