Download - Applications of PPI
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Applications of PPI
A/D - Temperature Sensor
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Analog to Digital
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Vin Range
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Timing
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Interfacing ADC
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Example
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Temperature Sensor
LM34 Datasheet
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Handshaking IO ExamplePrinter Connection
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IO Base Address for LPT
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LPT Adresses
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Printer’s Ports
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8255 Mode Definition Summary
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Mode 0
• Provides simple input and output operations for each of the three ports. – No “handshaking” is required, data is simply
written to or read from a specified port.– Two 8-bit ports and two 4-bit ports.– Any port can be input or output.– Outputs are latched.– Inputs are not latched
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• Mode 1 Basic functional Definitions:– Two Groups (Group A and Group B).– Each group has one 8-bit data port and one 4-bit control/data port.– The 8-bit data port can be either input or output. Both inputs and outputs are latched.– The 4-bit port is used for control and status of the 8-bit data port.
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8255 mode 1 (output)
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Mode 1 – Control Signals
• Output Control Signal Definition– OBF (Output Buffer Full F/F). (C7 for A, C1 for B)
• The OBF output will go “low” to indicate that the CPU has written data out to the specified port.– A signal to the device that there is data to be read.
– ACK (Acknowledge Input). (C6 for A, C2 for B)• A “low” on this input informs the 8255 that the data from Port A
or Port B has been accepted. – A response from the peripheral device indicating that it has read the
data.– INTR (Interrupt Request). (C3 for A, C0 for B)
• A “high” on this output can be used to interrupt the CPU when an output device has accepted data transmitted by the CPU.
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Timing diagram for mode1(output)
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8255 mode 1 (input)
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Mode 1 – Control Signals
• Input Control Signal Definition– STB (Strobe Input). (C4 for A, C2 for B)
• A “low” on this input loads data into the input latch.– IBF (Input Buffer Full F/F) (C5 for A, C1 for B)
• A “high” on this output indicates that the data has been loaded into the input latch; in essence, an acknowledgement from the 8255 to the device.
– INTR (Interrupt Request) (C3 for A, C0 for B)• A “high” on this output can be used to interrupt the CPU when an
input device is requesting service.
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Timing diagram for mode1(input)
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• MODE 2 Basic Functional Definitions:– Used in Group A only.– One 8-bit, bi-directional bus port (Port A) and a 5-bit control port (Port C).– Both inputs and outputs are latched.– The 5-bit control port (Port C) is used for control and status for the 8-bit, bi-directional bus
port (Port A).
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Mode 2• Output Operations
– OBF (Output Buffer Full). The OBF output will go low to indicate that the CPU has written data out to port A.
– ACK (Acknowledge). A low on this input enables the tri-state output buffer of Port A to send out the data. Otherwise, the output buffer will be in the high impedance state.
• Input Operations– STB (Strobe Input). A low on this input loads data
into the input latch.– IBF (Input Buffer Full F/F). A high on this output
indicates that data has been loaded into the input latch.
Pin Function
PC7 /OBF
PC6 /ACK
PC5 IBF
PC4 /STB
PC3 INTR
PC2 I/O
PC1 I/O
PC0 I/O
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