Microchip Davidtait LM75.TXT
; LM75.ASM
;
; Written by Aaron Hickman <Aaron.Hickman@drexel.edu>
; Added to PIC archive: 21/May/1998
LIST p=16c84
#include <p16c84.inc>
__CONFIG 11h
CONSTANT VARS=0CH
CONSTANT SCL=7
CONSTANT SDA=6 ; bits on Portb defined
CONSTANT TX=5
DEVICE_ADR EQU VARS+0 ; A2 A1 A0 address
O_BYTE EQU VARS+1 ; byte sent on I2C bus
I_BYTE EQU VARS+2 ; byte received on I2C bus
_N EQU VARS+3 ; index
_25US_LOOP EQU VARS+4 ; timing
IN_BYTE_MSB EQU VARS+5
IN_BYTE_LSB EQU VARS+6
BCD_0 EQU VARS+7
BCD_1 EQU VARS+8
BCD_2 EQU VARS+9
COUNT EQU VARS+10
TEMP EQU VARS+11
DATA_BYTE EQU VARS+12
SEROUT_LP EQU VARS+13
BAUD_RATE EQU VARS+14
DELAY_A EQU VARS+15
DELAY_B EQU VARS+16
DELAY_LP1 EQU VARS+17
DELAY_LP2 EQU VARS+18
FRACTION EQU VARS+19
ORG 000H
MOVLW 90H
MOVWF DEVICE_ADR
MOVLW 0EH
MOVWF BAUD_RATE
CONFIG_PORTS:
BSF STATUS, RP0 ; select Bank 1
MOVLW 1FH ; PORTB bits 7,6 & 4 = outputs and 4-0 & 5 = inputs
MOVWF TRISB
BCF STATUS, RP0 ; select Bank 0
READ_LM75:
CALL START
MOVF DEVICE_ADR, W
IORLW 01H
MOVWF O_BYTE
CALL OUT_BYTE
CALL NACK
CALL IN_BYTE
CALL ACK
MOVF I_BYTE, W
MOVWF IN_BYTE_LSB
CALL IN_BYTE
CALL NACK
CALL STOP
MOVF I_BYTE, W
MOVWF FRACTION
CLRF IN_BYTE_MSB
MOVLW 0CH
CALL DISPLAY
BTFSS IN_BYTE_LSB, 7
GOTO POSITIVE
MOVLW '-'
CALL DISPLAY
COMF IN_BYTE_LSB, W
MOVWF IN_BYTE_LSB
GOTO FINISHUP
POSITIVE:
MOVLW '+'
CALL DISPLAY
FINISHUP:
CALL BIN_BCD
MOVF BCD_1, W
CALL ASCII_LOW
CALL DISPLAY
MOVF BCD_2, W
CALL ASCII_HIGH
CALL DISPLAY
MOVF BCD_2, W
CALL ASCII_LOW
CALL DISPLAY
MOVLW '.'
CALL DISPLAY
BTFSC FRACTION, 7
MOVLW '5'
BTFSS FRACTION, 7
MOVLW '0'
CALL DISPLAY
MOVLW 0xDF
CALL DISPLAY
MOVLW 'C'
CALL DISPLAY
CALL DELAY
CALL DELAY
GOTO READ_LM75
DISPLAY:
CALL OUT_SER_CHAR
CALL DELAY_100US
RETURN
;************************************************************************
; The BCD values resulting from the CONVERT subroutine *
; are transmited via RS-232 protocol to a PC using the *
; following subroutine. The 8-bit values are sent using *
; the 8,N,1 format at 9600 baud (assuming a 2MHz ceramic *
; clock). *
;************************************************************************
OUT_SER_CHAR:
MOVWF DATA_BYTE
MOVLW .9
MOVWF SEROUT_LP
BCF STATUS, C
SEROUT1:
BTFSC STATUS, C
BCF PORTB, TX
BTFSS STATUS, C
BSF PORTB, TX
MOVFW BAUD_RATE
MOVWF DELAY_A
MOVFW BAUD_RATE
MOVWF DELAY_B
SEROUT2:
DECFSZ DELAY_A, F
GOTO SEROUT2
RRF DATA_BYTE, F
DECFSZ SEROUT_LP, F
GOTO SEROUT1
BCF PORTB, TX
NOP
NOP
SEROUT3:
DECFSZ DELAY_B, F
GOTO SEROUT3
NOP
RETURN
;**********************************************************************
; Unpack the BCD values stored in R1 and R2, ignoring R0. *
;**********************************************************************
ASCII_HIGH:
ANDLW 0xF0
MOVWF DATA_BYTE
SWAPF DATA_BYTE, W
ADDLW 30H
RETURN
ASCII_LOW:
ANDLW 0x0F
ADDLW 30H
RETURN
;************************************************************
; Delay subroutine for general use. *
;************************************************************
DELAY:
MOVLW 0xFF
MOVWF DELAY_LP1
DELAY_1:
MOVLW 0xFF
MOVWF DELAY_LP2
DELAY_2:
NOP
DECFSZ DELAY_LP2, F
GOTO DELAY_2
DECFSZ DELAY_LP1, F
GOTO DELAY_1
RETURN
DELAY_100US:
MOVLW .20
MOVWF DELAY_LP1
DELAY_100US_1:
NOP
NOP
DECFSZ DELAY_LP1, F
GOTO DELAY_100US_1
RETURN
;****************************************************************
; This routine converts a 16 bit binary number *
; to a 5 digit BCD number. The 16 bit binary *
; input locations are IN_BYTE_MSB and IN_BYTE_LSB. *
; The 5 digit BCD number is returned in BCD_0, *
; BCD_1 and BCD_2 with BCD_0 containing the most *
; significant digit in the low order nibble. *
;****************************************************************
BIN_BCD:
BCF STATUS, 0
MOVLW 10H
MOVWF COUNT
CLRF BCD_0
CLRF BCD_1
CLRF BCD_2
LOOP16:
RLF IN_BYTE_LSB, F
RLF IN_BYTE_MSB, F
RLF BCD_2, F
RLF BCD_1, F
RLF BCD_0, F
DECFSZ COUNT, F
GOTO ADJ_DEC
RETLW 0
ADJ_DEC:
MOVLW BCD_2
MOVWF FSR
CALL ADJ_BCD
MOVLW BCD_1
MOVWF FSR
CALL ADJ_BCD
MOVLW BCD_0
MOVWF FSR
CALL ADJ_BCD
GOTO LOOP16
ADJ_BCD:
MOVLW 3
ADDWF 0, W
MOVWF TEMP
BTFSC TEMP, 3
MOVWF 0
MOVLW 30
ADDWF 0, W
MOVWF TEMP
BTFSC TEMP, 7
MOVWF 0
RETLW 0
; The following routines are low level I2C routines applicable to most
; interfaces with I2C devices.
IN_BYTE ; read byte on i2c bus
CLRF I_BYTE
MOVLW .8
MOVWF _N ; set index to 8
CALL HIGH_SDA ; be sure SDA is configured as input
IN_BIT
CALL HIGH_SCL ; clock high
BTFSS PORTB, SDA ; test SDA bit
GOTO IN_ZERO
GOTO IN_ONE
IN_ZERO
BCF STATUS, C ; clear any carry
RLF I_BYTE, F ; i_byte = i_byte <lt 1 | 0
GOTO CONT_IN
IN_ONE
BCF STATUS, C ; clear any carry
RLF I_BYTE, F
INCF I_BYTE, F ; i_byte = (i_byte <lt 1) | 1
GOTO CONT_IN
CONT_IN
CALL LOW_SCL ; bring clock low
DECFSZ _N, F ; decrement index
GOTO IN_BIT
RETURN
;**********************************************
OUT_BYTE: ; send o_byte on I2C bus
MOVLW .8
MOVWF _N
OUT_BIT:
BCF STATUS,C ; clear carry
RLF O_BYTE, F ; left shift, most sig bit is now in carry
BTFSS STATUS, C ; if one, send a one
GOTO OUT_ZERO
GOTO OUT_ONE
OUT_ZERO:
CALL LOW_SDA ; SDA at zero
CALL CLOCK_PULSE
CALL HIGH_SDA
GOTO OUT_CONT
OUT_ONE:
CALL HIGH_SDA ; SDA at logic one
CALL CLOCK_PULSE
GOTO OUT_CONT
OUT_CONT:
DECFSZ _N, F ; decrement index
GOTO OUT_BIT
RETURN
NACK: ; bring SDA high and clock
CALL HIGH_SDA
CALL CLOCK_PULSE
RETURN
ACK:
CALL LOW_SDA
CALL CLOCK_PULSE
RETURN
START:
CALL LOW_SCL
CALL HIGH_SDA
CALL HIGH_SCL
CALL LOW_SDA ; bring SDA low while SCL is high
CALL LOW_SCL
RETURN
STOP:
CALL LOW_SCL
CALL LOW_SDA
CALL HIGH_SCL
CALL HIGH_SDA ; bring SDA high while SCL is high
CALL LOW_SCL
RETURN
CLOCK_PULSE: ; SCL momentarily to logic one
CALL HIGH_SCL
CALL LOW_SCL
RETURN
HIGH_SDA: ; high impedance by making SDA an input
BSF STATUS, RP0 ; bank 1
BSF TRISB, SDA ; make SDA pin an input
BCF STATUS, RP0 ; back to bank 0
CALL DELAY_SHORT
RETURN
LOW_SDA:
BCF PORTB, SDA
BSF STATUS, RP0 ; bank 1
BCF TRISB, SDA ; make SDA pin an output
BCF STATUS, RP0 ; back to bank 0
CALL DELAY_SHORT
RETURN
HIGH_SCL:
BSF STATUS, RP0 ; bank 1
BSF TRISB, SCL ; make SCL pin an input
BCF STATUS, RP0 ; back to bank 0
CALL DELAY_SHORT
RETURN
LOW_SCL:
BCF PORTB, SCL
BSF STATUS, RP0 ; bank 1
BCF TRISB, SCL ; make SCL pin an output
BCF STATUS, RP0 ; back to bank 0
CALL DELAY_SHORT
RETURN
DELAY_SHORT: ; provides nominal 25 usec delay
MOVLW .5
MOVWF _25US_LOOP
DELAY_SHORT_1:
NOP
DECFSZ _25US_LOOP, F
GOTO DELAY_SHORT_1
RETURN
END
| file: /Techref/microchip/davidtait/lm75.txt, 10KB, , updated: 2001/4/17 11:15, local time: 2024/12/25 21:19,
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