| UMBC | CMSC 391 -- Programming Microcontrollers |
| Instruction | Nr of Cycles | Number of Executions | Total Cylces |
|---|---|---|---|
lcall delay | 2 | 1 | 2 |
delay: mov r0, dpl | 1 | 1 | 1 |
00001$: mov r1, #230 | 1 | 1 | 1 |
00002$: nop | 1 | 230 | 230 |
nop | 1 | 230 | 230 |
nop | 1 | 230 | 230 |
nop | 1 | 230 | 230 |
nop | 1 | 230 | 230 |
nop | 1 | 230 | 230 |
djnz r1, 00002$ | 2 | 230 | 460 |
djnz r0, 00001$ | 2 | 1 | 2 |
ret | 2 | 1 | 2 |
That gives a total of 1056 cycles. The formula for calculating the times is:
1848 x 12
Tinsts = --------------------------
22,118,400 per second
I came up with a delay of 0.0010026 seconds, or 1.0026 milliseconds.
Actual delay - Desired delay
Terror = -----------------------------
Desired delay
That gives us:
1.0026 - 1.0000
Terror = ---------------- = 0.26%
1.0000
One quarter of one percent, that is good! Isn't it?What are the requirements? If you are to perform a task for five milliseconds, plus or minus one percent, this represents failure. Back to the drawing board!
This is also not a good solution for another reason. While this delay is being performed, the microcontroller can do nothing else. (Of course, that may or not be a bad thing, especially if you have nothing else to do.
But what happens if there is an interrupt? There goes the our timing, right down the drain.
If I want to use a 16-bit value in Timer1 for timing purposes (the largest possible using only one timer), the time delay is calculated:
(12 * (65,536 -InitValue))
TimeDelay = -------------------------
22,118,400
InitValue = TL1 + (256 * TH1)
We will set up the timer and set up the interrupt, and then do whatever else we would like to do.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Equates ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
0000: .EQU MODE16, 0x33
0000: .EQU TIMER1, 40h
;82C55 memory locations, Rev 4
0000: .equ port_a, 0xF800 ;access port A
0000: .equ port_b, 0xF801 ;access port B
0000: .equ port_c, 0xF802 ;access port C
0000: .equ port_abc_pgm, 0xF803 ;configure in/out of all th
0000: .equ port_d, 0xF900 ;access port D
0000: .equ port_e, 0xF901 ;access port E
0000: .equ port_f, 0xF902 ;access port F
0000: .equ port_def_pgm, 0xF903 ;configure in/out of all th
; Useful routines in PAULMON2 that you can call. When you
; later want a stand-alone application, you can copy them
; from the PAULMON2 source code (or write you own if you lik
0000: .equ cout, 0x0030 ;print byte in acc to seria
0000: .equ cin, 0x0032 ;get byte from serial port
0000: .equ phex, 0x0034 ;print acc in hex (2 digits
0000: .equ phex16, 0x0036 ;print dptr in hex (4 digit
0000: .equ pstr, 0x0038 ;print a string @dptr
0000: .equ esc, 0x003E ;paulmon2's check for esc k
0000: .equ newline, 0x0048 ;print a newline (CR and LF
0000: .equ pint8u, 0x004D ;print acc as unsigned int
0000: .equ pint16u, 0x0053 ;print dptr as unsigned int
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Code ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
2000: .org 2000h
2000: 80 49 sjmp startup
;
; We are going to take advantage of PAULMON2 interrupt handl
; Except for the interrupt timer 1, simply output a message
; the name of the interrupt. That would demostrate that the
; worked if we wished to test it.
;
2003: .org 0x2003
2003: 90 20 6A mov dptr, #ie0msg
2006: 12 00 38 lcall pstr
2009: 32 reti
200B: .org 0x200B
200B: 90 20 6F mov dptr, #tf0msg
200E: 12 00 38 lcall pstr
2011: 32 reti
2013: .org 0x2013
2013: 90 20 74 mov dptr, #ie1msg
2016: 12 00 38 lcall pstr
2019: 32 reti
201B: .org 0x201B
201B: 80 0D sjmp tf1handler
201D: 32 reti
2023: .org 0x2023
2023: 90 20 7E mov dptr, #sermsg
2026: 12 00 38 lcall pstr
2029: 32 reti
tf1handler:
202A: D5 01 10 djnz 1, skipping
202D: EF mov a, R7
202E: 04 inc a
202F: FF mov R7, a
2030: 11 3E acall ledout
2032: 75 01 1C mov 1, #1Ch
2035: 75 8B 00 mov TL1, #0
2038: 75 8D 00 mov TH1, #0
203B: C2 8F clr TF1
skipping:
203D: 32 reti
ledout:
203E: C0 83 push dph
2040: C0 82 push dpl
2042: 90 F9 01 mov dptr, #port_e
2045: F0 movx @dptr, a
2046: D0 82 pop dpl
2048: D0 83 pop dph
204A: 22 ret
startup:
;
; Set up the LEDs
;
204B: 90 F9 03 mov dptr, #port_def_pgm
204E: 74 80 mov a, #128
2050: F0 movx @dptr, a ;make all D-E-F port pins o
;
; Set up registers
;
2051: 7F 00 mov R7, #0h ; Value to display
2053: 79 1D mov R1, #1Dh ; Need to overflow this man
;
; Set up the timers. We need 1C2000h machine cycles, so
; the first time through so that we only do it 2000h t
; 0000 - 2000 = 0E000
; We will then have to the loop 1D times to get to our
;
2055: 75 8B 00 mov TL1, #0
2058: 75 8D E0 mov TH1, #0E0h
;
; Set up the Interrupts
;
;
; Set up TMOD SFR -- NOT BIT ADDRESSABLE
;
205B: 85 33 89 mov TMOD, MODE16 ; Set it up as a 16-bit tim
;
; Set up TCON SFR -- Start the time
;
205E: 85 40 88 mov TCON, TIMER1
;
; Set up TCON
;
2061: D2 8E setb TR1 ; Start your engines
;
; Set up IE
;
2063: D2 AB setb ET1
2065: D2 AF setb EA
;
; Just to prove that we can do something else and
; let the timers do the work, we will do nothing,
; once everything has been initialized. Now it
; is up to the interrupt handler.
;
foo:
2067: 80 FE sjmp foo
2069: 22 ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Data ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
206A: 49 45 30 0D
00 ie0msg: .db "IE0", 13, 0
206F: 54 46 30 0D
00 tf0msg: .db "TF0", 13, 0
2074: 49 45 31 0D
00 ie1msg: .db "IE1", 13, 0
2079: 54 46 31 0D
00 tf1msg: .db "TF1", 13, 0
207E: 53 45 52 49
41 4C 0D 00
sermsg: .db "SERIAL", 13, 0