CSC270 Homework 10
--D. Thiebaut 18:51, 14 April 2009 (UTC)
UNDER CONSTRUCTION
Problem #1
This picture is taken from the following Web site: http://www.sbprojects.com/knowledge/ir/nec.htm .
It depicts part of a broader protocol for sending commands over infrared communication between a remote device and a receiver (consumer electronics device).
You will notice that to send a '1', the remot actually sends a burst (about 21 cycles) of a signal with a frequency of 38 KHz, followed by a gap with no activity with a duration of 2.25 ms - 560 us. Similarly, to send a '0', the remote sends the same burst of 38KHz (about 26 cycles), followed by a shorter gap of 1.12 ms - 560 us.
Write the assembly function that can be called to send a '1'. In other words, if we replaced your LED by an infrared LED, what is the program that the 6811 would have to execute to generate the first part of the waveform shown above?
Same question, but this time for sending a '0'.
If you put an RTS instruction at the end of your function, and call the first function SendOne, and the second function SendZero, then you can write something like this:
;--------------------------------------------------------------------
; SendAsciiNEC.asm
; takes the ascii code stored in the byte variable data and sends it
; to output port at address 8000, which we assume is connected to an
; infrared LED.
; The protocole used is that of the NEC corporation, and fully described
; in http://www.sbprojects.com/knowledge/ir/nec.htm .
;
; All 8 bits are sent, one after the other.
; The program returns to the monitor when finished.
;
; The starting point is at label Start.
;
org 0000
saveB FCB 0 ; variable to save AccB in
data FCB 'A' ; ascii code for 'A'
;--------------------------------------------------------------------
; MAIN PROGRAM
; All 8 bits stored in byte data are sent, one after the other.
;
org 0010
start: ldab #8 ; get ready to send 8 bits
loop: ldaa data ; get byte to send
anda #1 ; get the least significant bit of Acca
cmpa #1 ; is it 1?
beq send1 ; if so go send a 1
jsr SendZero; if not, send a 0
jmp testEnd ; go to end of loop
Send1: jsr SendOne ; send a 1
testEnd: ldaa Data ; get data
lsra ; shift Acca 1 bit to the right
staa Data ; save it back in data
decb ; decrement AccB
cmpb #0 ; is it 0 yet?
bne loop ; no, still more bits to send
jmp C000 ; done, return control to Monitor
;--------------------------------------------------------------------
; SendOne: sends a '0' to the InfraRed LED at Port Address
; 8000 using the NEC protocole presented at
; http://www.sbprojects.com/knowledge/ir/nec.htm .
; ACCB is not modified by the procedure.
; ACCA is very likely modified by the procedure.
SendOne: stab saveB ; save AccB
; your code goes here
.
.
.
ldab saveB ; restore AccB
rts
;--------------------------------------------------------------------
; SendOne: sends a '1' to the InfraRed LED at Port Address
; 8000 using the NEC protocole presented at
; http://www.sbprojects.com/knowledge/ir/nec.htm .
; ACCB is not modified by the procedure.
; ACCA is very likely modified by the procedure.
SendZero: stab saveB ; save AccB
; your code goes here
.
.
.
ldab saveB ; restore AccB
rts
