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resources:seven_seg [2019/07/01 14:24] jgoeders |
resources:seven_seg [2019/10/23 09:14] (current) jgoeders [Module Description] |
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| The challenge we have is deciding how long to drive each anode signal. If the “on” time of the anode signals is too long, the eye and brain will detect that only one digit is being displayed at a time and we will see the digits turn on and then off in sequential order. If the “on” time is just right, human brain will perceive all four characters as being displayed at the same time through persistence of vision. | The challenge we have is deciding how long to drive each anode signal. If the “on” time of the anode signals is too long, the eye and brain will detect that only one digit is being displayed at a time and we will see the digits turn on and then off in sequential order. If the “on” time is just right, human brain will perceive all four characters as being displayed at the same time through persistence of vision. | ||
| - | The easiest way to sequence through the eight different digits is to create a "free running" counter. A free running counter is a counter that increments continuously at each clock cycle (See Figure 16.6). When the free running counter reaches all 1's, it will then roll over to zero on the next clock cycle. The top three bits of this free running counter will cycle through the digits, while the rest of the bits of the counter will determine the amount of time to display each digit. For example, if you used an 8-bit counter then the top three bits of the counter would determine which digit to display and the bottom 5 bits would be used to count the duration that each digit is displayed. With 5 bits, each digit will be displayed for 2<sup>5</sup> = 32 clock cycles. | + | The easiest way to sequence through the eight different digits is to create a "free running" counter. A free running counter is a counter that increments continuously at each clock cycle (See Figure 16.6). When the free running counter reaches all 1's, it will then roll over to zero on the next clock cycle. The top three bits of this free running counter will cycle through the digits, while the rest of the bits of the counter will determine the amount of time to display each digit. For example, **suppose** you used an 8-bit counter. Then, the top three bits of the counter would determine which digit to display and the bottom 5 bits would be used to count the duration that each digit is displayed. With 5 bits, each digit will be displayed for 2<sup>5</sup> = 32 clock cycles. |
| The table below summarizes how the top three bits of this free running counter are used to select the appropriate digit in the display: | The table below summarizes how the top three bits of this free running counter are used to select the appropriate digit in the display: | ||
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| The clock we have on the NEXYS 4 board runs at 100 MHz with a clock period of 10 ns. | The clock we have on the NEXYS 4 board runs at 100 MHz with a clock period of 10 ns. | ||
| If you use an eight-bit counter to sequence the digits as described above, the top three bits would be used to sequence through each digit and the bottom five bits would be used to count the number of clock cycles to display each digit. Thus, each digit would be displayed for 2<sup>5</sup> x 10 ns = 320 ns. (The module provided below does not use an 8-bit counter, this is just described here as an example). | If you use an eight-bit counter to sequence the digits as described above, the top three bits would be used to sequence through each digit and the bottom five bits would be used to count the number of clock cycles to display each digit. Thus, each digit would be displayed for 2<sup>5</sup> x 10 ns = 320 ns. (The module provided below does not use an 8-bit counter, this is just described here as an example). | ||
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| + | The actual module given to you does not use an 8-bit counter, but instead the counter width is parameterizable. Look at the SystemVerilog below to see the default width of the counter. | ||
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| The controller has the following three important inputs: | The controller has the following three important inputs: | ||
| - | * **Data input (32 bits):** Each digit can display 4-bits of data. With eight digits, the seven segment display can display up to 32-bits of data. You provide a 32-bit data input that indicates what data to display on all 8 of the digits. | + | * **''dataIn'' (32 bits):** Each digit can display 4-bits of data. With eight digits, the seven segment display can display up to 32-bits of data. You provide a 32-bit data input that indicates what data to display on all 8 of the digits. |
| - | * **Digit Display (8 bits):** The seven segment controller does not need to turn on all eight digits of the display all of the time. In some applications, you may only want to display four of the eight digits (when there is only 16-bits of data to display). The controller can "turn off" or disable individual digits of the display by never asserting their corresponding Anode signals. This digit display input will have one bit for each digit of the display. A '1' in this bit indicates that the controller should turn on the digit, while a '0' turns off the digit. | + | * **''digitDisplay'' (8 bits):** The seven segment controller does not need to turn on all eight digits of the display all of the time. In some applications, you may only want to display four of the eight digits (when there is only 16-bits of data to display). The controller can "turn off" or disable individual digits of the display by never asserting their corresponding Anode signals. This digit display input will have one bit for each digit of the display. A '1' in this bit indicates that the controller should turn on the digit, while a '0' turns off the digit. For example, if you always want all digits to be turned on, you can connect ''8'b11111111'' to the ''digitDisplay'' port. |
| - | * **Digit Point (8 bits):** There is one digit point in the bottom right corner of each digit of the seven segment display and there is a corresponding cathode signal for this digit point. This 8-bit input indicates which of the digit points of the display you are to highlight. There is one bit for each of the digits in the display. A '1' indicates that the corresponding digit point should be turned on and a '0' indicates that the corresponding digit point should be turned off. | + | * **''digitPoint'' (8 bits):** There is one digit point in the bottom right corner of each digit of the seven segment display and there is a corresponding cathode signal for this digit point. This 8-bit input indicates which of the digit points of the display you are to highlight. There is one bit for each of the digits in the display. A '1' indicates that the corresponding digit point should be turned on and a '0' indicates that the corresponding digit point should be turned off. For example, if you only want the leftmost digit point lit up, you can connect 8'b10000000 to the ''digitPoint'' port. |
| Full list of ports for this module: | Full list of ports for this module: | ||
