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Serial Interface 7135 to 8751 Reads Analog ValuesuC Input and Output I/O is Keyboard and LCD when you
build a Calculator
or a Text/Morse Communicator. When you control a motor it is
Drive/Speed and Direction for Motor and Tacho or Opto Counters for
Feedback. In both cases you have Input and Output which is Logic or
Analog which has to reach the CPU. Getting the analog into the uC is done here with
ICL7135, with a simple two wire serial interface. Here a Pair of CD4538
MMV is used to shape the pulse just right for uC data transfer, The Busy signal and clock when anded (AND) will give a burst of pulses. Count them and deduct 10,001 from the virtual uC counter. This is the reading. See ICL7135 at Maxim IC.  |
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| Serial Interface 7135 to 8751 Reads Analog Values - del20001 |
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| U2B sends a short interrupt pulse to uC which means 'busy' of 7135 has gone from high to low and reading in counter of uC is valid, also reset counter to 0 for new reading next time 'busy' goes high. count the clock and substract 10,001 from that, you got a reading. BUSY 'AND' CLK '-' 10,001 '=' READING ICL7135 Pin 11 +5V, Pin 1 -5V, Pin 24 digital GND The input of ICL7135 has to be protected from Overvoltage both negative and positive. This is done by a Clamping circuit made of two back to back low leakage Zeners. Some zeners may leak more, see the datasheet. Use Ordinary Diode clamping circuit with 2 nos 1N4148 in series to the + and - rails. Change ICL7135 to 200mV FS for Diode Clamping.  Related Resources - |