.
Fig 6.a
For circuit details download the circuit
diagram file. Though reading into circuit is little
stressful but gives more insight into how the ports are
connected.
The display used is a common anode type RED display unit
, which is connected to the MCU through a Low-Voltage Octal
Bus Buffer (inverted), TC74LCX240F.
So now what we have do is, to find out the Hexadecimal
code word for each number (from 0 to 9) to get displayed
on the 7-segment LED display unit.
| Port |
Segment |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
0 |
| PF 0 |
A |
OFF |
ON |
ON |
OFF |
ON |
ON |
ON |
ON |
ON |
ON |
| PF 1 |
B |
ON |
ON |
ON |
ON |
OFF |
OFF |
ON |
ON |
ON |
ON |
| PF 2 |
C |
ON |
OFF |
ON |
ON |
ON |
ON |
ON |
ON |
ON |
ON |
| PF 3 |
D |
OFF |
ON |
ON |
OFF |
ON |
ON |
OFF |
ON |
OFF |
ON |
| PF 4 |
E |
OFF |
ON |
OFF |
OFF |
OFF |
ON |
OFF |
ON |
OFF |
ON |
| PF 5 |
F |
OFF |
OFF |
OFF |
ON |
ON |
ON |
OFF |
ON |
ON |
ON |
| PD 3 |
G |
OFF |
ON |
ON |
ON |
ON |
ON |
OFF |
ON |
ON |
OFF |
| PD 4 |
dp |
X |
X |
X |
X |
X |
X |
X |
X |
X |
X |
Chart 1
The above chart (chart 1) provides the information on which
output lines/pins to be made high or low to display the
corresponding numbers. We have not used dp (decimal point)
segment and so is the status given as 'X' meaning don't
care.
Now, let us figure out the hexadecimal code for each number.
For example let us take the number "2". From
the chart given above, it can be understood that, to display
2, we need to make a, b, d, e & g segments of the display
"HIGH" and the remaining segments "LOW".
Thus the GPIO output registers PF & PD should hold
the data values as shown below.
| Bit |
PF5 |
PF4 |
PF3 |
PF2 |
PF1 |
PF0 |
| Data |
X |
1 |
1 |
0 |
1 |
1 |
| Bit |
PD5 |
PD4 |
PD3 |
PD2 |
PD1 |
PD0 |
| Data |
X |
0 |
1 |
X |
X |
X |
X - Don't care
Here let's assume to substitute X with 0 (zero). The hexadecimal
equivalent of "011011" is "1B" and that
of "001000" is "08". So to display the
digit "2" we need to load 1B to the register
of the port PF and 08 to the register of the port PD.
Similarly we can find out the hexadecimal equivalent code
for each digit to be displayed.
Once we got the Hexadecimal code for each number, it is
time to move to the programming section. Here are the basic
steps to be followed.
- As we did in the Module-4 , copy the TestLED directory
as COUNTER. Now you would have COUNTER folder as well
in "C:\ame51gnu\Examples\674051" directory
- Rename theTestLED.c in this directory as counter.c
- Open the counter.c file with "Notepad++" or
any other text editor and delete all the content and insert
the following code in this file
int main(void)
{
int i;
volatile unsigned char * ModeRegister1;
volatile unsigned char * OutputRegister1;
volatile unsigned char * ModeRegister2;
volatile unsigned char * OutputRegister2;
ModeRegister1 = 0xB7A05008; // PF GPIO mode register address
in Hex
OutputRegister1 = 0xB7A05000; // PF GPIO output register
address in Hex
ModeRegister2 = 0xB7A03008; // PD GPIO mode register address
in Hex
OutputRegister2 = 0xB7A03000; // PD GPIO output register
address in Hex
*ModeRegister1 =0x00FF; // Configure Port F bit 0 as output
*ModeRegister2 =0x00FF; // Configure Port D bit 0 as output
while (1)
{
*OutputRegister1 = 0x003F; // Display 0
*OutputRegister2 = 0x0000; // Display 0
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x0006; // Display 1
*OutputRegister2 = 0x0000; // Display 1
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x001B; // Display 2
*OutputRegister2 = 0x0008; // Display 2
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x000F; // Display 3
*OutputRegister2 = 0x0008; // Display 3
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x0026; // Display 4
*OutputRegister2 = 0x0008; // Display 4
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x002D; // Display 5
*OutputRegister2 = 0x0008; // Display 5
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x003D; // Display 6
*OutputRegister2 = 0x0008; // Display 6
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x0007; // Display 7
*OutputRegister2 = 0x0000; // Display 7
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x003F; // Display 8
*OutputRegister2 = 0x0008; // Display 8
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x0027; // Display 9
*OutputRegister2 = 0x0008; // Display 9
for (i=0; i<1000000; i++); //Delay
}
}
5. Now compile and run the program by following the same
steps as given in module -4.
6. Follow the procedures to load the program into the board
as mentioned in module-4 or read this user
manual.
Now you should see the 7-segment LED display, counting
from 0 to 9 and repeats the same.
You might have already got an idea about the ARM chipset
used in this kit, different ports, bits, different type
of modes in which it can operate (or can be configured),
and how to use the mode register & output register to
make the MCU to work according to our needs. Same kind of
configuration is done in this sample program also, except
the registers used are PF & PD.
Sample Program 3: Simultaneously
display decimal numbers from 0-9 in the seven segment display
and lighting the three LEDs available on the board/kit.
The following fig (Fig 6.b) shows the connectivity of the
3 LEDs (Green, Red & Yellow) to the Micro controller
ports.
Fig 6.b
Hope you remember that we used the port PE in the sample
program in module 4.
Same port is used here too to connect the three LEDs to
the MCU.
And also, as you saw in the previous sample program in
this module (module 6), the ports PF & PD are used for
the 7-segment display unit to get connected to the MCU.
So let us do it in a different way. Make the green LED
to glow when the 7-segment displays digits '2' and '4',
both green & yellow LEDs to glow while displaying '5',
'6' and '7' and all the three LEDs to glow while displaying
'8' and '9' on the 7-segment display.
So let us configure the output register of the port PE
for the three LED to work along with the 7-segment display
unit.
As you can see in the fig 6.b, the port bitsPE0, PE1 &
PE2 are used to drive the red, Yellow & green LEDs respectively.
And remember they are wired (in the kit) as "active
low".
| Bit |
PE6 |
PE5 |
PE4 |
PE3 |
PE2 |
PE1 |
PE0 |
| Data |
X |
X |
X |
X |
0 |
0 |
0 |
Suppose we want to glow the three LEDs at a time. For this,
all the three bits PE0, PE1 & PE2
are made Low (0) (bits PE3 to PE6 kept as "Dontcare"
in this case)
Its clear that the hexadecimal code to display all the
three LEDs is 00 and to make all of them OFF, the code is
07.
Now its time to focus on the program code. Let us change
the previous program as show below.
int main(void)
{
int i;
volatile unsigned char * ModeRegister1;
volatile unsigned char * OutputRegister1;
volatile unsigned char * ModeRegister2;
volatile unsigned char * OutputRegister2;
volatile unsigned char * ModeRegister3;
volatile unsigned char * OutputRegister3;
ModeRegister1 = 0xB7A05008; // PF GPIO mode register address
in Hex
OutputRegister1 = 0xB7A05000; // PF GPIO output register
address in Hex
ModeRegister2 = 0xB7A03008; // PD GPIO mode register address
in Hex
OutputRegister2 = 0xB7A03000; // PD GPIO output register
address in Hex
ModeRegister3 = 0xB7A04008; // PE GPIO mode register address
in Hex
OutputRegister3 = 0xB7A04000; // PE GPIO output register
address in Hex
*ModeRegister1 =0x00FF; // Configure Port Fbit 0 as outuput
*ModeRegister2 =0x00FF; // Configure Port D bit 0 as outuput
*ModeRegister3 =0x00FF; // Configure Port E bit 0 as output
while (1)
{
*OutputRegister1 = 0x003F; // display 0
*OutputRegister2 = 0x0000; // display 0
*OutputRegister3 = 0x0007; // all the three LEDs OFF
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x0006; // Display 1
*OutputRegister2 = 0x0000; // display 1
*OutputRegister3 = 0x0007; // all the three LEDs OFF
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x001B; // display 2
*OutputRegister2 = 0x0008; // display 2
*OutputRegister3 = 0x0003; //Green LED ON
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x000F; // display 3
*OutputRegister2 = 0x0008; // display 3
*OutputRegister3 = 0x0003; //Green LED ON
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x0026; // display 4
*OutputRegister2 = 0x0008; // display 4
*OutputRegister3 = 0x0003; //Green LED ON
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x002D; // display 5
*OutputRegister2 = 0x0008; // display 5
*OutputRegister3 = 0x0001; // Green & Red LEDs ON
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x003D; // display 6
*OutputRegister2 = 0x0008; // display 6
*OutputRegister3 = 0x0001; // Green & Yellow LEDs ON
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x0007; // display 7
*OutputRegister2 = 0x0000; // display 7
*OutputRegister3 = 0x0001; // Green & Yellow LEDs ON
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x003F; // display 8
*OutputRegister2 = 0x0008; // display 8
*OutputRegister3 = 0x0000; //green, Yellow, & Red LEDs
ON
for (i=0; i<1000000; i++); //Delay
*OutputRegister1 = 0x0027; // dis9
*OutputRegister2 = 0x0008; // dis9
*OutputRegister3 = 0x0000; //green, Yellow, & Red LEDs
ON
for (i=0; i<1000000; i++); //Delay
}
}
Now what you have to do is just edit the "counter.c"
file in the COUNTER folder and alter the program as shown
in the above code, or copy this program entirely to the
counter.c file after deleting the previous code . compile
and run the code as explained along with the previous sample
programs. Now you can see the LED getting on in the planned
sequence while the seven segment is displaying 0 to 9.
Now its times to write your own program?
Write an easy program to display
hexadecimal numbers F to 0 in decremental order.
Next Module
- 7(Serial communications -basic)
Previous Module
- 5(Architecture of ARM7 processor)
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