| 摘要 |
<p>PURPOSE:To obtain a interface circuit capable of bidirectional data transmission by forming a transmission transistor in open collector constitution with respect to an external equipment with a diode in-between, and by connecting it to an input terminal of an input signal level interface circuit. CONSTITUTION:An IF circuit 2 is added to a conventional IF circuit 1, and a signal OUT and a terminal IN are made common. When a data is inputted from an external equipment 1, voltage levels of GND -12V and GND +12V are inpressed to a terminal SIG 4, and the output of the circuit 1 is converted to a binary signal of Vss and Vdd to be transmitted to a CPU 5. And the titled equipment is so constituted that, at the time of input of said signal 1, the output from the CPU is maintained High, and at the time of input, a PNPTR 14 is maintained in off, so that an input data is subjected to no influence. When outputting, the output 16 of the CPU outputs the binary signal of Vdd and Vss to control on/off of the transistor TR14. The circuit 2 is constituted as open collector with respect to an external equipment, and a signal is transmitted through the external equipment 19, terminal 3, TR14, diode 13 and the terminal 4. Accordingly, when the output 16 of the CPU is High, only the voltage of a power supply source 17 at the terminal 4 becomes of a potential lower then the GND. And when the output 16 becomes low, the potential of the terminal 4 becomes High.</p> |
