of ATMEL in practical examples.
Calculating a keypad resistor matrix with avr_sim
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AVR-Single-Chip-Processors AT90S, ATtiny, ATmega of ATMEL in practical examples. Calculating a keypad resistor matrix with avr_sim |
The first entry in the "Project" menu is "New". If you
start, select this. Later on the once started project will be available
under "Open previous".
Then this window opens. We enter a project name, e.g. "resistor matrix",
by clicking into the editor field for the project location we select a folder
for that and we click on the two fields to get a "Short version" and
a "Linear program". We can then enter the target device either by
selecting it with the two drop-down fields to the left, if we already know
which AVR type we like to have, or by clicking on "Device selector"
on the right if we are unsure which types can do what we need.
With the device selector we mark a one on the ADC drop-down field, to which
the resistor matrix shall be connected to.
Several AVR types ares available in more than one package type. We are
now asked to select from one of these types. The three radio buttons
(or two or four depending from the type) select one of those packages.
The button "Show picture" shows us the type in the selected
package as picture.
Now avr_sim has constructed a short template of an Assembler program.
The editor shows this, and allows to add or change the source code.
By pressing the key F2 we can add the hardware of the device as ASCII
text.
When selecting this, the simulator window opens. Here we mark, in the
section "Show internal hardware", the field "ADC".
The ADC window offers the following possibilities for entries:
The resistor matrix window shows this here. You can click on lots of
selections, most the entries are self-explaining. Those who want more
detailed information can consult the avr_sim-handbook's chapter on the
resistor matrix. There you'll find detailed explanations on what is
behind the selector "Use int. VRef", what you'll get with
"View data table" enabled, what "View voltages"
does and what happens if you click onto one of the resistors of the
resistors table.
Main:
; Set the ADLAR bit to enable 8-bit conversion,
; note that the ADLAR bit in a tiny13 is in the ADMUX
; port register, other devices place this bit elsewhere
ldi rmp,(1<<ADLAR)|(1<<MUX1) ; 8-bit ADC, select ADC channel input
out ADMUX,rmp
; Enable the ADC, start conversion, AD prescaler = 128
ldi rmp,(1<<ADEN)|(1<<ADSC)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0)
out ADCSRA,rmp
WaitAdc:
sbic ADCSRA,ADSC ; Wait for ADSC bit to get clear
rjmp WaitAdc ; ADSC bit not yet cleared, continue waiting
in rmp,ADCH ; Read the MSB of the result
Loop:
rjmp loop
If we assemble and start the simulator, we can set a breakpoint
to the line with "rjmp loop" by clicking into the gutter
area of this line. This allows to use "Run/Go" instead of
single stepping through the code. With this, the active conversion
field in the ADC window moves faster than with single steps.
Because the ADC's clock is divided by 128, the conversion needs
1.39 Milliseconds. The result appears in the ADC window as
left-adjusted byte (ADCH) and in register R16: a zero. Just because
we didn't set the channel's voltage to a more interesting value yet.
If we display the R-matrix, we can set it to 16 keys, the vertical
resistors as single, and the 1% entry has already been set. Now we
press "Optimize" several times, and hopefully end with
zero overlaps (if not: restart the iteration), and if we click on
the key 1 in the schematic, we'll get the 571.1 mV onto our
ADC channel (in the ADC window). The table says that the key '1'
produces an 8-bit ADC value of 29.
Indeed: the correct result of the conversion appears. The only
question left is: how can we get the "1" from the 29?
For this we click on one of the eight resistors in the table and
we'll get the message that an include file has been saved, which
can be included into our source code with the line ".include
"resistormatrix.inc" behind the line "rjmp loop".