User manual

Basys MX3™ Board Reference Manual
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Page 22 of 56
A scanning display controller circuit can be used to show a 4-digit number on this display. This circuit drives the
anode signals and corresponding cathode patterns of each digit in a repeating, continuous succession at an update
rate that is faster than the human eye can detect. Each digit is illuminated just one-fourth of the time, but because
the eye cannot perceive the darkening of a digit before it is illuminated again, the digit appears continuously
illuminated. If the update, or “refresh”, rate is slowed to around 45Hz, a flicker can be noticed on the display.
To make each of the four digits appear bright and continuously illuminated, all should be driven once every 1 to
16ms, with a refresh frequency of about 1kHz to 60Hz. For example, if every digit is refreshed every 3ms,
corresponding to a frequency of 333Hz, the entire display will be refreshed every 12ms. The controller must drive
low the cathodes with the correct pattern when the corresponding anode signal is driven high.
To illustrate the process:
1. If AN0 is asserted while CB and CC are asserted, then a “1” will be displayed in digit position 1.
2. If AN1 is asserted while CA, CB, and CC are asserted, a “7” will be displayed in digit position 2.
3. If AN0, CB, and CC are driven for 4ms, and then AN1, CA, CB, and CC are driven for 4ms in an endless
succession, the display will show “71” in the first two digits. An example timing diagram for a four-digit
controller is shown in Fig. 7.4.
AN0
AN1
AN2
AN3
Cathodes
Digit 0
Refresh period = 1ms to 16ms
Digit period = Refresh / 4
Digit 1 Digit 2 Digit 3
Figure 7.4. 4-digit scanning display controller timing diagram.
Please note that the two dots (situated between the middle digits) are not connected.
7.1 Connectivity
Name
PIC32 Pin
Description
AN0
AN12/PMA11/RB12
Anode 0 pin
AN1
AN13/PMA10/RB13
Anode 1 pin
AN2
VREF-/CVREF-/PMA7/RA9
Anode 2 pin
AN3
VREF+/CVREF+/PMA6/RA10
Anode 3 pin
CA
TRD1/RG12
Cathode A pin
CB
RPA14/RA14
Cathode B pin
CC
PMD14/RD6
Cathode C pin
CD
TRD0/RG13
Cathode D pin
CE
RG15
Cathode E pin
CF
PMD15/RD7
Cathode F pin
CG
PMD13/RD13
Cathode G pin
DP
TRD2/RG14
Cathode DP (decimal point)
pin
Table 7.1. Seven-segment connectivity.