Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement - Manual (Page 169)

High-Speed Microcontroller User’s
Guide: Network Microcontroller
Supplement
169
SETTING UP THE 1-WIRE MASTER
The first step is to determine the input crystal frequency to the DS80C400. Next, look up the appropriate divider ratio for that frequen-
cy in DS80C400 data sheet. This value, along with a logic 1 for the most significant bit, must be input into the clock divisor register
that, in turn, enables the input clock and divides it down to the proper frequency. The following code demonstrates enabling the clock
divider for a frequency of 10MHz.
MOV OWMAD, #004h ; Setup the address pointer
MOV OWMDR, #086h ; Set CLK_EN, and set divisor to 10MHz
SENDING A 1-WIRE RESET
The following code sends out a 1-Wire reset, waits for an interrupt to signal it has finished, and then checks the results to see if a part
was located.
ORG 43h
LJMP Interrupt
ORG 100h
.
.
Owrst:
MOV OWMAD, #003h ; Set the address pointer to the Interrupt Enable register
MOV OWMDR, #001h ; Enable the PD interrupt
MOV OWMAD, #005h ; Set the address pointer to the Control register
MOV OWMDR, #080h ; Set EOWMI to enable the OW interrupts
MOV OWMAD, #000h ; Set the address pointer to the Command register
MOV OWMDR, #001h ; Enable a 1-Wire Reset
MOV IE, #080h; Enable the 400’s interrupts
MOV EIE, #01h ; Enable external interrupts 2-5 as well as OWMI
LCALL Wait4int ; Call the wait routine
MOV OWMAD, #002h ; Set the address pointer to the Interrupt register
MOV A, OWMDR ; Read the value of the Interrupt register
ANL A, #002h ; Mask off all bits but the PD Result bit
CJNE A, #02h, Pdloop ; Check to see if a part was found, loop again if not
LJMP Cont ; Continue on with your program
Pdloop:
LJMP Owrst ; perform 1-Wire Reset again
Cont:
.
.
Wait4int:
MOV R1, #000h ; Clear flag
Waitloop:
MOV A, R1 ; Obtain the value in R1
CJNE A, #01h, Waitloop; ; Check flag and keep looping until set
RET
Interrupt:
MOV EXIF, #08h ; Turn off INT5 flag
MOV R1, #001h; Set loop flag
RETI
END
SENDING A BYTE
The following code can be used in conjunction with the 1-Wire reset code to send out a byte across the 1-Wire line. In order to read a
byte, the same program is used, but the byte value to send should be 0FFh. This, in turn, produces eight write 1’s, which are the same
as eight read-time slots.
MOV OWMAD, #003h ; Set the address pointer to the Interrupt Enable register
MOV OWMDR, #010h ; Enable the RBF interrupt
MOV OWMAD, #001h ; Set the address pointer to the TX/RX register
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