Description
ECE 362 – Experiment 6 Rev 2/14 Bigger Bytes Lab Manual
Experiment 6: “Big > 10” Football Play Clock
Instructional Objectives:
· To illustrate how an external interrupt device flag can be realized
· To illustrate use of port pins as both inputs and outputs
Parts Required:
· From “DK-2” parts kit (used in ECE 270)
breadboard and wire
DIP switch and pull-up SIP
LEDs
ten 150 W resistors
· From “DK-3” parts kit
two common anode 7-segment displays (one is included in DK-2 parts kit)
one 22V10 PLD (or equivalent) – also included in DK-2 parts kit
Preparation:
· Read this document in its entirety
· Complete the pre-lab steps and have them available for your instructor to check
Introduction
The “Big > Ten” has a problem. Plagued by an ever-expanding roster of “marginal” football teams whose games seem to drag on forever (especially where one of the teams gets behind by, say, 42 points before the end of the first half), coach Boris Badenov of recently added Whatsamatta U has proposed a new rule that will help speed up these adventures in boredom:
reduce the play clock time (i.e., the time allotted to line up and call the next play) to the number of teams that will be in the “Big > Ten” Conference effective 2014 (as of this writing, looks like 14). This change from the current 40/25 second rule has the potential to significantly reduce the boredom quotient (BQ) associated with the current football experience. Before Boris can get his billion-dollar bonus for coming up with such a brilliant idea, however, he needs to demonstrate a working prototype. Lucky for BB, there are a bevy of Boilermakers armed with 9S12C32
microcontroller kits (along with a few surviving parts from their earlier digital life), betting their design will better the BQ of boisterous Boilermaker fans watching bloviating quarterbacks.
Hardware Overview
Your job is to implement a 14-second play clock, i.e., a timer that when reset is loaded with the
value 14 (displayed on two 7-segment LEDs) and count down in one second intervals until 1.0
second remains, at which point it will count down in 0.1 second intervals from 1.0 to .0.
The function of the play clock timer will be controlled by the two pushbuttons on the docking
module: the left pushbutton (“PAD7”) should reset the play clock to 14 seconds (at the end of
every play), while the right pushbutton (“PAD6”) should start/stop the play clock (team calls a
time out). The left LED on your docking board (connected to port pin “PT1”) should be on
when the play clock is in the “run” state and off when it is in the “stop” state; the right LED
(connected to port pin “PT0”) should be turned on when the count reaches “.0”. Note that the
clock should stop counting down once it reaches .0, and that the right LED should remain on
until the play clock is reset.
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A GAL22V10 PLD will be used to realize all the “glue” logic for this experiment. The function
of each Port T pin used in this design is listed in Table 1.
Table 1. 9S12C32 Port T Connections to GAL22V10
9S12C32 Port T Function GAL22V10 Pin
PT2 tens (“half”) digit* 2 (input)
PT3 middle decimal point 3 (input)
PT4 BCD ones digit, least significant bit (D0) 4 (input)
PT5 BCD ones digit (D1) 5 (input)
PT6 BCD ones digit (D2) 6 (input)
PT7 BCD ones digit, most significant bit (D3) 7 (input)
* tens digit is either “1” (segments b and c of 7-segment display on) or blank, and therefore can
be controlled by a single bit
One of the functions the GAL22V10 will be programmed to perform is a BCD-to-display-code
conversion for the “ones digit”, as illustrated on page 19 of the ECE 270 Module 2 Lecture
Summary notes. It will also be used to buffer/drive the middle decimal point (on the two-digit
display) and the “tens (half) digit”. Since common-anode 7-segment displays will be used, the
corresponding output pins on the GAL22V10 will be programmed as active low. Note that a
150W current limiting resistor should be used between each LED cathode and GAL22V10 output
pin (the LED anodes will all be connected to +5 V). Output pins of the GAL22V10 used to drive
the display are listed in Table 2.
Table 2. GAL22V10 LED Display Outputs
GAL22V10 Pin* Destination
14 (com, output) segments b and c of tens digit
15 (com, output) middle decimal point
16 (com, output) segment a of one’s digit
17 (com, output) segment b of one’s digit
18 (com, output) segment c of one’s digit
19 (com, output) segment d of one’s digit
20 (com, output) segment e of one’s digit
21 (com, output) segment f of one’s digit
22 (com, output) segment g of one’s digit
* all active low – a 150W current limiting resistor is
required between each LED cathode and PLD pin
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The second function the GAL22V10 will be programmed to realize is an interrupt device flag for
the timing function. Here, a 10 Hz interrupt source will be provided by the function generator at
your lab station (use its SYNC output only, which provides a CMOS-compatible square wave
signal at the frequency of interest). This external clocking signal will be connected to the CLK
input of the GAL22V10 (pin 1), which will then cause a flip-flop within the PLD (“device flag”)
to set on positive (low-to-high) clock edges. The active low device flag output (pin 23) will be
connected to the IRQ¢ input of the 9S12C32 (port PE, pin 1). The device flag flip-flop will be
asynchronously cleared (by the interrupt service routine) via port M, pin 3 (programmed as an
output pin via the DDRM register). These connections are summarized in Table 3.
Table 3. 9S12C32 Port E Connections to GAL22V10
Source Function GAL22V10 Pin
9S12C32 PM3 (output) asynchronous clear of device flag (active high) 8 (input)
9S12C32 PE1 (input) CPU IRQ (active low) 23 (reg, output)
Function Generator
SYNC (output)
10 Hz interrupt request (positive edge) 1 (input)
Software Overview
Once the boot-up and initialization sequence is completed, the “main” program should simply
“loop” − looking at various “flags” (SRAM locations used as Boolean variables) to see if some
action should be taken (this is sometimes called “state machine” code organization). Four such
flags will be needed: (a) the “tenth second” flag, (b) the left pushbutton (“reset shot clock”) flag,
(c) the right pushbutton (“start/stop”) flag, and (d) the “run/stop” flag. Note that the timer value
should be stored as two “packed” BCD bytes, with an “implied decimal point” between the
“ones” and “tenths” digit. For example, the value of the timer when reset should be 014.0 (stored
as $0140); after the first interrupt (while the “run” flag is set), this value should be decremented
to 013.9 (stored as $0139), i.e., the (4-digit) timer value should be decremented by one (in BCD)
every time an IRQ interrupt occurs (while the “run” flag is set). Note that the 4-digit BCD value
can be decremented by adding $99 to each packed byte (starting with the low order byte),
followed by a DAA.
The main program logic should be organized as follows:
If the “tenth second” (IRQ interrupt) flag is set, the following actions should take place:
clear the “tenth second” (IRQ interrupt) flag
if the “run/stop” flag is set (i.e., play clock is running), then
decrement the play clock by one tenth of a second
update the seven-segment display
if the time remaining is 10 seconds or more, display the tens and ones digits
if the time remaining is less than 10 seconds but more than 1.0 second, blank the
tens display digit and only display the ones digit
if the time remaining is less than 1.0 second, turn on the “middle” decimal point
and display the tenths digit instead of the ones digit
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If the left pushbutton (“reset play clock”) flag is set, the following actions should take place:
clear the left pushbutton flag
clear the “run/stop” flag
turn off both the “run/stop” and “time expired” LEDs (on the docking module)
reset the display to 14
If the right pushbutton (“start/stop”) flag is set, the following actions should take place:
clear the right pushbutton flag
toggle the “run/stop” flag
toggle the “run/stop” LED (on the docking module)
The main program should also, in its polling loop, check to see if the play clock has reached .0;
if it has, the following actions should take place:
clear the “run/stop” flag
turn on the “time expired” LED (on the docking module)
turn off the “run/stop” LED (on the docking module)
In addition to decrementing the timer value stored in memory (while the “run” flag is set), the
IRQ interrupt service routine is also used to “sample” the pushbuttons and set the corresponding
“pushbutton flags” accordingly (note that this will require an additional variable in memory to
track the pushbutton’s previous state).
if the previous state of the left pushbutton was high and its current state is low (note that
the pushbuttons are momentary contact closures to ground, and that their default state is
“high”), set the “reset play clock” flag
if the previous state of the right pushbutton was high and its current state is low, set the
“run/stop” flag
Pre-Lab Step 1. Interface Glue Logic
Write an ABEL or Verilog program for a GAL22V10 that realizes the interface glue logic
described in the Hardware Overview. Compile your program using ispLever and program your
device using the universal programmer at your lab station (review your ECE 270 Lab Manual if
you have forgotten how to do this).
To test your glue logic design, connect the two 7-segment displays to your GAL22V10 as
described in Table 2. Use a DIP switch (recalling the need for a pull-up SIP) to provide test
inputs to pins 1-8 of the GAL22V10. Finally, connect a “loose” (spare) LED to pin 23 of the
GAL22V10 (the active low IRQ signal), which you may want to leave in place for debugging
purposes). Now you should be able to test the combinational BCD-to-display-code decoding
functionality, the tens (half-digit) display, the middle decimal point, and the operation of the
device flag (set by a low-to-high transition of CLK, cleared by an asynchronous reset).
Once you have verified the operation of your interface logic and display circuitry, remove the
DIP switch (and its associated pull-up SIP) from your breadboard and install your
microcontroller board. Note that you should only proceed if your glue logic circuitry is
functioning correctly – attempting to write code at this point will prove to be otherwise futile!
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Pre-Lab Step 2. Schematic/Wiring
Complete the wiring diagram below, based on information provided in Tables 1-3. Be sure to
include the requisite LED current limiting resistors (total of ten 150W resistors required). After
your TA has checked your schematic, connect your microcontroller module to the GAL22V10 as
described in Tables 1 and 3.
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Step 1. Coding
Complete the ASM skeleton file provided on the course website. Note that the “finished product”
should work in a “turn key” fashion, i.e., your application code should be stored in flash memory
and begin running upon power-on or reset.
Step 2. Demonstration
Demonstrate your working hardware and software to your lab TA, and be prepared to explain
your answers to the Thought Questions (below).
Step 3. Thought Questions
Answer the following thought questions in the space provided below:
(a) Why do we need to know the previous state of the pushbuttons, and set “flags” based on
their transition from high to low?
(b) Did you notice any “anomalous” behavior as a result of the relatively low (10 Hz) rate at
which the pushbuttons are sampled? If so, what do you think might be a more appropriate
sampling rate?
