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This statement reads the first ID from the 1wire bus into a variable(array).





var2 = 1WSEARCHFIRST( port , pin)





A variable or array that should be at least 8 bytes long that will be assigned with the 8 byte ID from the first 1wire device on the bus.


The PIN port name like PINB or PIND.


The pin number of the port. In the range from 0-7. Maybe a numeric constant or variable.


The 1wireSearchFirst() function must be called once to initiate the ID retrieval process. After the 1wireSearchFirst() function is used you should use successive function calls to the 1wSearchNext function to retrieve other ID's on the bus.


A string can not be assigned to get the values from the bus. This because a null may be returned as a value and the null is also used as a string terminator.


I would advice to use a byte array as shown in the example.


The 1wirecount function will take 4 bytes of SRAM.

___1w_bitstorage , Byte used for bit storage :

lastdeviceflag bit 0

id_bit bit 1

cmp_id_bit bit 2

search_dir bit 3

___1wid_bit_number, Byte

___1wlast_zero, Byte

___1wlast_discrepancy , Byte





The following asm routines are called from mcs.lib.

_1wire_Search_First : (calls _1WIRE, _ADJUST_PIN , _ADJUST_BIT_ADDRESS)

Parameters passed : R24 : pin number, R30 : port , X : address of target array

Returns nothing.



See also







'name                     : 1wireSearch.bas

'copyright                : (c) 1995-2021, MCS Electronics

'purpose                  : demonstrates 1wsearch

'micro                    : Mega48

'suited for demo          : yes

'commercial addon needed  : no



$regfile = "m48def.dat"

$crystal = 4000000


$hwstack = 32                       ' default use 32 for the hardware stack

$swstack = 10                       'default use 10 for the SW stack

$framesize = 40                     'default use 40 for the frame space


Config 1wire = Portb.0               'use this pin

'On the STK200 jumper B.0 must be inserted


'The following internal bytes are used by the scan routines

'___1w_bitstorage , Byte used for bit storage :

'      lastdeviceflag bit 0

'      id_bit         bit 1

'      cmp_id_bit     bit 2

'      search_dir     bit 3

'___1wid_bit_number, Byte

'___1wlast_zero,  Byte

'___1wlast_discrepancy , Byte

'___1wire_data , string * 7 (8 bytes)


'[DIM variables used]

'we need some space from at least 8 bytes to store the ID

Dim Reg_no(8) As Byte


'we need a loop counter and a word/integer for counting the ID's on the bus

Dim I As Byte , W As Word


'Now search for the first device on the bus

Reg_no(1) = 1wsearchfirst()


For I = 1 To 8                                             'print the number

  Print Hex(reg_no(i));





'Now search for other devices

Reg_no(1) = 1wsearchnext()

For I = 1 To 8

  Print Hex(reg_no(i));



Loop Until Err = 1




'When ERR = 1 is returned it means that no device is found anymore

'You could also count the number of devices

W = 1wirecount()

'It is IMPORTANT that the 1wirecount function returns a word/integer

'So the result variable must be of the type word or integer

'But you may assign it to a byte or long too of course

Print W



'as a bonus the next routine :

' first fill the array with an existing number

Reg_no(1) = 1wsearchfirst()

' unremark next line to chance a byte to test the ERR flag

'Reg_no(1) = 2

'now verify if the number exists

1wverify Reg_no(1)

Print Err

'err =1 when the ID passed n reg_no() does NOT exist

' optinal call it with pinnumber line  1wverify reg_no(1),pinb,1


'As for the other 1wire statements/functions, you can provide the port and pin number as anoption

'W = 1wirecount(pinb , 1)                                    'for example look at pin PINB.1