Input from Port D

1
Input from Port D
In this project, we will use port D as input and
port A as output, by connecting three input bits
of port D to logic switches, and connecting three
output bits of port A to LEDs. Your assignment
will be to extend the program we worked on in the
last lab. Port_a bits 4,5,6 for output, will be
wired to LEDs (as before). Port_d bits 2,3,4 for
input, will be wired to three of the 0-1 logic
switches on the IDL-800.
2
MicroStamp Pin Functions
Note Port D bits 0 1 are used by the serial
cable to download our programs. Do not use.
3
Exclusive OR

• A useful function for complementing bits is the
  Exclusive-OR operation, often abbreviated as XOR.
  Our assembly language has EORA and EORB.
• 1100
• XOR 0110
• ------
• 1010
• The XOR puts in 1 in the output if either inputs
  are 1, BUT NOT BOTH!

4
Complementing with XOR

• XOR can be used to complement bits
• Say we want to complement bit 2, but we dont
  know (and dont care) what bit two currently is

(bits) 3,2,1,0 Original 1101
XOR with 0100 ------ Result 1001
(bits) 3,2,1,0 changed 1001
XOR with 0100 ------ Result 1101

• Only the bit desired is flipped, all other bits,
  regardless of whether they are 0 or 1, are
  unchanged.

5
You may choose to use SW0-2
6
Example inputtst.asm
This is the same example program as before. It
is NOT the solution to the last lab!
7
Example cont.
8
Example cont.
9
Your Assignment for Next Monday

• Lab Preparation
• If your program from the last lab, did not work
  correctly, continue to work with and debug that
  program using the wookie. In either case, revise
  your program to use the XOR operation (EORA or
  EORB).
• Next, modify your WORKING program, so that the
  input PD_2 controls PA_4 output determining how
  fast PA_4 flashes. 0-slow, 1-fast. The other
  inputs/outputs work to echo the state of the
  switches without flashing.
• PD3 ? PA5
• PD4 ? PA6
• Test your program on the wookie.
• Modify your program to work on the
  68HC11/Microstamp.
• Hands-On portion next Monday
• Wire your input switches, assembly, download, and
  test/debug your program from step 4 on the
  MicroStamp.
• Demonstrate your working program to your
  instructor.