Digilent 410-126P - Manual (Page 2)

PmodSSD Reference Manual Digilent, Inc.
www.digilentinc.com Copyright Digilent, Inc. Page 2
digit in a repeating, continuous succession, at
an update rate that is faster than the human
eye can respond. Each digit is illuminated one-
half 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 a given point
(around 45 hertz), then most people will begin
to see the display flicker.
In order for each of the four digits to appear
bright and continuously illuminated, both digits
should be driven once every 1 to 16ms (for a
refresh frequency of 1KHz to 60Hz). For
example, in a 60Hz refresh scheme, the entire
display would be refreshed once every 16ms,
and each digit would be illuminated for ½ of the
refresh cycle, or 8ms. The controller must
assure that the correct anode pattern is
present when the corresponding cathode
signal is driven. To illustrate the process, if
Cat1 is asserted while AB and AC are
asserted, then a “1” will be displayed in digit
position 1. Then, if Cat2 is asserted while AA,
AB and AC are asserted, then a “7” will be
displayed in digit position 2. If Cat1 and AB,
AC are driven for 8ms, and then Cat2 and AA,
AB, AC are driven for 8ms in an endless
succession, the display will show “17”. An
example timing diagram for a two-digit
controller is shown below.
An un-illuminated seven-segment display, and nine
illumination patterns corresponding to decimal digits
A
F
E
D
C
G
Individual anodes
Common cathode
Two-digit Seven
Segment Display
B
Cat1
Cat2
Anodes
Refresh period:
1ms to 16ms
Digit period:
Refresh / 2
Digit 1 Digit 0 Digit 0