KND-08 and KND 44
8 DIGITS NUMERIC DISPLAY CARDS
|KND-08 - 7 segment LED display.|
Any fans of electronic sooner or later has to affront, and
easily solve, the problem of visual segnalations management.
As long as we have to manage few electric bulbs or few LEDs the problem is not so hard. In fact there are many suitable demos as for example the TIO 16 within it's possible to undertake and to test severals exercises.
When instead there are a lot of elements to manage it is neccesary to have several powerful and efficient solutions. For this reason why, this article shows how 8 digits LED display plus 6 segnalation LEDs can be managed.
LEDs DISPLAY CONTROLLER: SGS THOMSON M5480
The KND xx cards are based on the comfortable M5480. This component
includes all the driving circuits for for a maximum of 23
The driving is based on a constant current generator that is incorporated in the package. With this features you can set the brightness as you prefer, by simply changing a resistor value.
From a fast count You discover that while the M5480 can drive only 23 LEDs, this card actually has 70 LEDs that must be individually managed.
Don't worry: a circuit trick and a little bit of firmware will help us.
Looking at the electric diagram of the circuit you can see that the M5480 doesn't drive all the digits contemporaneously but in groups of two.
So the firmware must drive these four digits couples in a sequential cyclic mode. The drive operation divided in different sections is named "Multiplexing" while the periodic display drive is named "Refresh".
|fig. 3 - KND-44 card Diagram.|
As you can see from the electric diagram and from the possible
read of SGS-THOMSON data sheets, the hardware result easily
to understand. Remain to clarify what must be done witt the management
First we have to clarify that this circuit is general and it can be used with any kind of CPU.
On the contrary there are difference for the the software, or firmware, in fact they depend on the programming language and on the used microprocessor.
I have performed a general choice by selecting the BASCOM (described on July/August, n° 196 issue) combined with one of the numerous 8051 based CPUs or the really fast AVR RISC microprocessor. In detail, for this selection are available the examples for some cards as the GPC F2, that many of you has already mounted, starting from the relative kit.
By using these information and the numerous comments of the programs, everybody can use these programs as a starting point to generate the application with different programming language or with another CPU
INTERRUPT MANAGEMENT WITH BASCOM
The use of an efficient and flexible programming language as
the BASIC compiler BASCOM,
let the user solve even the rougher problems.
An example is the semplicity for the refresh's display interrupt management. A counter is loaded to generate a periodic interrupt, each 20 msec, that updates the displayed data. At the end of the refresh interrupt routine, the CPU goes on with the execution of the main program.
The refresh's operation holds the CPU's execution time that basically depends from the algorithm efficency and from the CPU work frequency.
|KND-44 - 7 segment LED display.|
This card, available in two versions: with 8 digits on the
same line or with two independent lines by 4 digits, allows to
rapidly obtain a display for numeric visualization, using only
2 output lines at TTL level. In both the versions are always managed
also 6 signalization LEDs.
The driving of the display controller is made through a syncronous communication line with standard Clock and Data signals.
The management CPU, for example the GPC F2 card, serializes data through two digital lines connected to Clock and Data signals in a way that load the M5480 internal shift register, with the right valve for the 23 outputs.
This operation, repeated every 20 msec, allows, thaks to the effect of picture persisting on the eyes retina, to correctly see value on all the displays, without flicking problems.
For further information on M5480 functionality, I advise to read the proper SGS-Thomson data sheets.
- SGS THOMSON M5480
Page up-dated at August 29, 2004
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