Digilent DIO5 - Manual (Page 7)

DIO5 Reference Manual Digilent, Inc.
www.digilentinc.com Page 7
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Seven-Segment LED display
The DIO5 board contains a modular 4-digit,
common anode seven-segment LED display.
In a common anode display, the seven anodes
of the LEDs forming each digit are connected
to four common circuit nodes (labeled A1
through A4 on the DIO5). Each anode, and
therefore each digit, can be independently
turned on and off by driving these signals to a
‘1’ or a ‘0’. The cathodes of similar segments
on all four displays are also connected
together into seven common circuit nodes
labeled CA through CG. Thus, each cathode
for all four displays can be turned on and off
independently.
This connection scheme creates a multiplexed
display, where driving the anode signals and
corresponding cathode patterns of each digit in
a repeating, continuous succession can create a 4-digit display. In order for each of the four
digits to appear bright and continuously
illuminated, all four digits should be driven once
every 1 to 16ms (for a refresh frequency of 1KHz
to 60Hz). For example, in a 60Hz refresh
scheme, each digit would be illuminated for ¼ of
the refresh cycle, or 4ms. The controller must
assure that the correct cathode pattern is
present when the corresponding anode signal is
driven. To illustrate the process, if A1 is driven
high while CB and CC are driven low, then a “1”
will be displayed in digit position 2. Then, if A2 is
driven high while CA, CB and CC are driven low,
then a “7” will be displayed in digit position 2. If
A1 and CB, CC are driven for 4ms, and then A2
and CA, CB, CC are driven for 4ms in an
endless succession, the display will show “17” in
the first two digits. An example timing diagram is
provided below.
Anodes are connected via
transistors for greater current
A4
Vdd
a b c d e f g dp
A3 A2 A1
Cathodes are connected to
Xilinx device via 100
Ω resistors
Seven-segment display detail and cathaode
patterns to display the decimal digits.
Common anode Digit Illuminated Segment
Shown a b c d e f g
0 1 1 1 1 1 1 0
1 0 1 1 0 0 0 0
2 1 1 0 1 1 0 1
3 1 1 1 1 0 0 1
4 0 1 1 0 0 1 1
5 1 0 1 1 0 1 1
6 1 0 1 1 1 1 1
7 1 1 1 0 0 0 0
8 1 1 1 1 1 1 1
9 1 1 1 1 0 1 1
a
f
e
d
c
b
g
a f g e d c b
A1
A2
A3
A4
Cathodes Digit 1 Digit 2 Digit 3 Digit 4
Refresh period = 1ms to 16ms
Digit period = Refresh / 4