Introduction
This discussion shows how to interface a Dallas Semiconductor DS1620 Thermometer with the Basic Stamp BS2.
Resources
A data sheet is available in Adobe .pdf format from . Devices are available from for about $5.00 each.
Discussion
The following discussion is in rough form. It will be reworked and eventually it will become a part of a new book which discuuses interfacing with serial devices. But, in the interim, you may find it useful.
Program DS_1620_1.BS2 illustrates how to write to the configuration register, start temperature conversions, read the temperature from the device and stop the temperature conversions so as to save power when temperature readings are not required.
The configuration register is configured in subroutine config_1621 by writing the command $0c followed by the data $02 to configure the 1621 in a CPU controlled mode with continuous temperature conversion. The temperature conversion process is then initiated in subroutine start_convert with the $ee command. Readings are then made in subroutine meas by sending the $aa command and then reading the nine bits from the 1621. After ten readings, the loop is exited and the conversion process is halted using subroutine stop_convert by sending the command $22.
My handling of the conversion to temperature by simply dividing the nine bits received from the 1621 by 2 is clumsy as it sacrifices the 0.5 resolution.
' DS1620_1.BS2
'
' Illustrates how to measure temperature using DS1620 3-Wire Thermometer
'
' BS2 DS1620
'
' Pin2 (term 7) -------------------- DQ (term 1)
' Pin1 (term 6) -------------------- CLk (term 2)
' Pin0 (term 5) -------------------- RST (term 3)
'
'
' Debug statements were included only to see what is going on.
'
' Program configures 1620 for CPU operation, starts conversion, makes
' 10 measurments and stop conversion.
'
' copyright H. Paul Roach, MSU, March 13, '97
'
o_byte var byte ' byte sent to DS1620
i_9_bit var word ' reaw temperature data from 1620
n var byte ' index
times var byte ' number of measurements
dirs = $f0ff
IN con 0
OUT con 1
RST con 0
CLK con 1
DQ con 2
DQ_OUT var out2
DQ_IN var in2
DQ_DIR var dir2
main
gosub config_1620 ' configure 1620
gosub start_convert ' continuous conversion
for times=1 to 10 ' make 10 measurments
gosub meas
T_C = i_9_bit/2
debug dec T_C
sleep 60 ' one minute between readings
next
gosub stop_convert ' stop conversion process to save power
stop
config_1620 ' send command $0c followed by $02 to configure
' for CPU mode
low RST
high CLK
high RST ' initiate by bringing RST high
o_byte = $0c
gosub out_byte
o_byte = $02
gosub out_byte
low RST
pause 200 ' give some time for the internal programming
return
start_convert ' send command $ee to cause continuous conversion
high CLK
high RST
o_byte = $ee
gosub out_byte
low RST
return
meas ' send command $aa to read data and then read
high CLK
high RST
o_byte = $aa
gosub out_byte
gosub read_9_bits
low RST
return
stop_convert ' send command $22 to stop the conversions
high CLK
high RST
o_byte = $22
gosub out_byte
low RST
return
out_byte ' outputs byte in o_byte, beginning with least
' significant bit
DQ_DIR=OUT
for n = 0 to 7
DQ_OUT = o_byte & $01 'least significant bit
low CLK
debug dec DQ_OUT
high CLK
o_byte = o_byte >> 1 'shift data 1 place right
next
debug 13
return
get_9_bits ' reads 9 bits from 1620 beginning with least
' significant bit
DQ_DIR = IN
i_9_bit = 0
for n = 0 to 8
low CLK
i_9_bit = (i_9_bit >> 1) | (DQ_IN << 8)
debug dec D_IN
high CLK
next
DQ_DIR=OUT
debug 13
return