7Segment Display and Count by 16

1
7-Segment Display and Count by 16

• This is our third lab using the 68HC11
  microcontroller.
• We will write a program that counts by 16 in a
  loop, using one of the registers to count in.
  Port A will display the count, and will be
  connected to the 7-segment LED display.
• You will need a floppy diskette to hold your
  programs, for later printing.

2
Lab Preparation A simp3v2.asm

• Examine simp2v2.asm to determine how the LEDs are
  being controlled in the loop.
• Determine the changes needed to modify the
  program, so that Port A will contain and display
  the contents of a register (bits 4,5,6 on pins
  4,5,6).
• Determine the changes needed to make your
  register count up by 16s.
• Since you will be displaying only 3-bits (4,5,6)
  of an 8-bit number in the register, explain in
  your notebook, how counting by 16 will work and
  what it will show on the 7-segment LED.
• During the lab, you will edit and modify a copy
  of simp2v2.asm to create count-16.asm. You will
  assemble count16.asm and download it into the
  MicroStamp board, for execution and testing.

3
MODIFIED simp2v2.asm

file simp2v2.asm This program
illustrates flashing PA6.. Dr. Hoganson,
10/2/02
org e000 beginning of
EEPROM (68HC811E2) rbase equ 0000 beginning of
register/memory port_a equ rbase0 port A is the
first register h_sec equ ffff delay loop value
(about 1/2 second)
begin ldaa
04 value to disable timed interrupt staa 3f
disables the timed interrupt lds ff set
stack start loop ldaa 40 write logic high to
PA6 (turn on LED) staa port_a 0 is location
of Port A bsr delay clr port_a clear
PortA bsr delay bra loop
Continued next slide
4
MODIFIED simple2.asm

delay loop subroutine

delay ldy h_sec delay loop (about 1/2
second) dloop dey iny extra iny,dey add delay
time dey bne dloop rts
org ff
fe define the reset vector to point to start of
program fdb begin begin is the start of the
program
5
Part B The Lab

• Record in your lab notebook, your observations
  for each of the following steps.
• Wire the 68HC11 as we did in the last lab, with
  power and ground, and LEDs connected to Port A
  bits 4,5,6.
• Wire three PortA outputs to the inputs to the
  decoder for the 7-segment display. Also wire a
  ground from one of the 7-seg displays.
• Verify correct operation by running the demo
  program, but also checking the wiring to the
  7-segment display.
• Edit, assemble, download, and test your
  count16.s19 program, and verify correct
  operation.
• You will need to save your program on your floppy
  diskette, and print out a listing of each
  program, which you will insert into your lab
  notebook.