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no response from senzor

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aral

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I connected a DS1820 temperature senzor to a ms430 ucontroler . The senzor is externally supplied (not parasite). I connected the grounds from senzor, msp430 and from my power supply together . I also have a 4.7K pullup resistor on my data line (discussed here https://www.electro-tech-online.com/threads/need-help-with-a-following-robot.15584/) .My wires are about 25 cm long . The initialisation procedure which the senzor requests is :

- During the initialization sequence the bus master (msp430)transmits (TX) the reset pulse by pulling the 1-wire bus
low for a minimum of 480 µs. The bus master(msp430) then releases the bus and goes into receive mode (RX).
When the bus is released, the 5k pullup resistor pulls the 1-wire bus high. When the DS18S20 detects
this rising edge, it waits 15–60 µs and then transmits a presence pulse by pulling the 1-wire bus low for
60–240 µs.

I put my asm source for the implementation of this initialization procedure below. For some reason the senzor doesn't respond with the presence pulse . Why doesn't the senzor respond ?

mov #01h,P0DIR ; set P0.0 as ouput portpin

MOV.B #0h,&P0OUT ; pull the bus low 480 us

mov #08h,r5;contor

label8:
mov #10h,r7 ;contor

label:

dec r7

jnz label
; aici se termina 60 us

dec r5

jnz label8
;480 us(actually 510 us by my calcutions) delay ends


BIC.B #01h,P0DIR ; Set P0.0 as input and release the bus

;----------------------------------------------------------
mov #10h,r11 ; contor

label1:

dec r11

jnz label1
; 60 us delay ends (time for 4,7 K resistor to pull the bus high)
;----------------------------------------------------------

;----------------------------------------------------------
; 60 us loop begins
mov #10h,r10

bucla1:

dec r10

jnz bucla1
; 60 us loop ends

MOV.B &P0IN,r5; read from P0.0 cause the presence pulse has to arrive ; it doesn't !!! THIS Is MY PROBLEM !!!
 

Attachments

  • init.txt
    931 bytes · Views: 270
I've never been into MSP430,but I've used 18B20 with 89S5x.It's quite simple to initialize the sensor.I have the flowchart of the procedure of my subroutine in the attachment.You may refer to it.
 

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  • reset.jpg
    reset.jpg
    29.8 KB · Views: 375
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