This
circuit is an interface between 89C52 of Atmel with 7135 of Intersil.
With
This circuit you can read analog data of both polarities you can change
the
range scale with extra circuits, you can store data on a EEPROM or send
them
to PC thru RS232 or Comm port.
Firmware
:
The
example code for display drive, comm port has been given in the other
projects
on this site. So I will just explain how you can get the data from 7135.
Initialization :
Set Port 0 and Port 1 all pins high by writing ones.
enable INT1
Data Acquisition:
On INT1 interrupt Check the state of P 0.4 or D5 digit 5 of 7135.
if P 0.4 is low then do not do anything.
if P 0.4 is high then read Port 0 and store them in say D5VAL "value of
D5".
Also in a place say DIGCNT "digit counter" store the number 5.
now interrupt occurs again .....
decrement DIGCNT to 4
and Port 0 value store in D4VAL.
.......... this goes on till DIGCNT comes to 1 then you got all the
data.
Lower nibble of Port 0 contains the BCD value of the digit.
Digit 5 is MSD and Digit 1 is LSD.
Upper nibble contains polarity, over range and under range.
P1.2 can be used as an output port to RUN-HOLD the 7135 if you want.
Keep it low to hold and a high pulse to get one reading or keep it high
to keep reading.