Intoduction
Currently I have two undergraduate students who are developing material on interfacing with I2C devices. This includes Dallas Semiconductor DS1621 - Digital Thermometer and Microchip 24LC32 32K EEPROM.
At present, we have have implemented random read and write functions for the EEPROM. Future development will focus routines for sequential reads and writes and and an illustration on how this may be used as an inexpensive data logger. We also plan to look at the new 65K serial EEPROMs.
Another discussion deals with interfacing the 24LC32 with a
The 24LC32 is available in an 8-pin DIP from Digikey (Digikey 32LC32/P-ND). This provides 4K bytes of data storage for a mere $3.00. Note that eight of these may be cascaded on the same two signal leads so as to provide 32 K bytes. Pretty amazing!
The user is referred to for a data sheet. Hopefully with the data sheet and the following snippet of code, the user can adapt the code to their specific application. Note that in order to enhance understanding I avoided such commands as shiftin and shiftout.
If there are other I2C devices that you would like us to look at, please send me e-mail.
I have just received a grant from the National Science Foundation to continue doing this kind of stuff with my students. If you find this material useful, an entry in my guest book or an e-mail would be greatly appreciated.
' 24LC32.BS2
'
' Illustrates how to write and read to and from 24LC32 32K EEPROM
'
' BS2 24LC32
'
' Pin5 (term 10) ------------------- SCL (term 6) ----- To Other
' Pin4 (term 9) -------------------- SDA (term 5) ----- 24LC32 Devices
'
' Note that 10K pullup resistors to +5VDC are required on both signal
leads.
'
' Note that the slave address is determined by A2 (term 3), A1 (term2)
' and A0 (term 1) on 24LC32. The above SCL and SDA leads may be multipled
' to eight devices, each strapped for a unique A2 A1 A0 setting.
'
' Debug and Pause statements were included only to see what is going on.
'
' copyright Peter H. Anderson, MSU, March 1, '97
'
address var word ' 000 0000 00000 - 111 1111 1111
device var byte ' device 0-7
dta var byte ' data to program
o_byte var byte ' byte to send to memory
i_byte var byte ' byte fetched from memory
n var byte ' index
b var bit ' bit
ack_bit var bit
SDA_PIN con 4
SCL_PIN con 5
SDA_OUT var out4
SCL_OUT var out5
SDA_IN var in4
SDA_DIR var dir4
OUT con 1
IN con 0
dirs=$f0ff
main
address=$341 ' program data 55 into address $341
device=0
dta=$55
gosub write_random_data 'write dta to address $341
gosub read_random_data 'read from same location
debug hex i_byte
stop
write_random_data 'writes specified data to specified address
agn
gosub start
o_byte=$a0 | (device << 1) ' 1 0 1 0 a2 a1 a0 0
gosub out_byte
gosub nack
o_byte= address >> 8 ' high byte of address
gosub out_byte
gosub nack
o_byte= address & $ff ' low byte of address
gosub out_byte
gosub nack
o_byte= dta ' data
gosub out_byte
gosub nack
gosub sstop
gosub ack ' ack polling
if ack_bit=1 then agn
return
read_random_data ' reads data from specified address
' returns in variable in_byte
gosub start
o_byte=$a0 | (device << 1) ' 1 0 1 0 a2 a1 a0 0
gosub out_byte
gosub nack
o_byte= address >> 8 ' high byte of address
gosub out_byte
gosub nack
o_byte= address & $ff ' low byte of address
gosub out_byte
gosub nack
gosub start
o_byte=$a0 | (device << 1) | $01' 1010 a2 a1 a0 1
gosub out_byte
gosub nack
gosub get_byte
gosub nack
gosub sstop
return
out_byte
low SDA_PIN
for n=0 to 7
b= (o_byte >> 7) & 1
if (b=1) then out_one
SDA_DIR=OUT
debug "0"
_clk
high SCL_PIN
pause 100
low SCL_PIN
pause 100
o_byte=o_byte << 1
next
SDA_DIR=IN
return
out_one
SDA_DIR=IN
debug "I"
goto _clk
get_byte
SDA_DIR=IN 'input
i_byte=0
for n=0 to 7
pause 200
high SCL_PIN
pause 200
i_byte=(i_byte << 1) | SDA_IN
debug dec SDA_IN
low SCL_PIN
next
SDA_DIR=OUT 'output
return
nack
SDA_DIR=IN ' input just in case
ack_bit=1
high SCL_PIN
ack_bit=SDA_IN
debug "A"
debug dec ack_bit
debug $0d
low SCL_PIN
SDA_DIR=OUT ' output
return
ack
debug "POLL"
gosub start
o_byte=$a0 | (device << 1)
gosub out_byte
gosub nack
return
start
high SDA_PIN
high SCL_PIN
debug "START"
debug $0d
low SDA_PIN 'bring SDA low while clock is high
low SCL_PIN
return
sstop
low SDA_PIN
high SCL_PIN
pause 10
high SDA_PIN 'bring SDA high while clock is high
debug "STOP"
debug $0d
return