Transcript Microprocessor Engineering - Sheffield Hallam University

Peripherals & I/O lines
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All the on-chip peripherals are configured and
controlled through Special Function Registers
(SFR)
Many of the SFR’s are bit addressable
The 111 I/O lines are arranged into Ports
Some port lines have multiple functions which
must be configured for correct operation of the
required function.
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Infineon 167 I/O Ports
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111 I/O lines with individual bit addressability
Tri-stated in input mode
Selectable input thresholds (not on all pins)
Push/pull or open drain output mode
Programmable port driver control
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M167CS Functional Block Diagram
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Digital I/O Ports
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Port is where data enters/leaves the system
Digital I/O lines are normally grouped into 8-bit
ports or possibly 16-bit ports
Ports must be configured for input or output
before they are used
Most ports allow a mixture of inputs and outputs
on the same port
Some microcontrollers have instructions that
access individual bits of a port
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M167 digital I/O ports
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Associated with a port is a DIRECTION register
and on some a Port output control
Port direction - '0' = input, '1' = output
Output control – '0' = Push/pull, '1' = open-drain
In Keil 'C' all the SFR's are defined in the header
file "c167cs.h" with the Infineon standard names
– is Port x
 DPx – is the Direction for Port x
 ODPx = Open Drain Control for Port x
 Px
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Typical Port Structure
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Output Driver Types
Push/Pull Output Driver
Open-Drain Output Driver
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Parallel Ports in u-Vision 2
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Using all bits of ports
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Outputs
 DP4
= 0xff; // Direction all outputs
 P4 = value8; // output value to all 8-bits
 DP2 = 0xffff;
 P2 = value16;
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Inputs
 DP6
= 0x00; //Direction all inputs
 x = P6; // Read all 8-bits into variable x
 x would normally be an unsigned char but could be
unsigned int
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Bit Manipulation in 'C'
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'C' bit operators (binary operators)
OP symbol
Description
&
AND
|
OR
^
XOR
>> n
shift bits right n places
<< n
shift bits left n places
y = y OP z; can be written as y OP= z;
E.g.'s
y = y & 0x80;
y = y >> 4;
y &= 0x80;
y >>= 4;
unary operator ~ complements (invert all bits)
e.g. y = ~y;
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Masking to achieve bit manipulations
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Masking uses AND and OR operators
Use OR ('|') to set bits to '1'
Use AND ('&') to set bits to 0
OR
AND
XOR
A
B Output
A
B Output
A
B Output
0
0
0
1
0
1
0
0
0
1
0
0
0
0
0
1
0
1
1
0
1
1
0
0
1
0
1
1
1
1
1
1
1
1
1
0
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Controlling output bits – Output Masking
Setting bits to 1 using OR (|)
 General format: Port = Port | mask;
 Mask has '1' to set a bit, '0' to leave bit unchanged.
Example: Set bit 3 to '1'
P4 = P4 | 0x08;
// 0x08 = 00001000 binary
 Setting bits to 0 using AND (&)
 General format: Port = Port & mask;
 Mask has '0' to clear a bit, and '1' to leave bit unchanged.
Example: Set bit 3 to '0'
P4 = P4 & 0xf7;
// 0xf7 = 11110111 binary
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Input Masking
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Use AND (&) and a mask to isolate a selected bit
Used in input Polling to test an individual input bit
Loop until a bit becomes logic '1'
while( (P4 & 0x08) == 0) { ; }
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Two possible results 00000000 or 00001000
I.e. zero or non-zero
Loop until a bit becomes logic '0'
while( (P4 & 0x08) != 0) { ; }
Often written as
while( P4 & 0x80); // in 'C' zero is FALSE, non-zero is
TRUE
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bit variables
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The Keil C compiler supports the bit addressable
features of Infineon microcontrollers
General declaration format
sbit bitname = Portx^y; // port x bit y
E.g.
sbit motor_dir = DP2^10;
sbit motor = P2^10;
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MUST declare sbit's before 'C' main() function
Using sbit's
motor_dir = 1;
motor = 1;
// Set bit to output
//turn on motor
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