The TL851 is an economical digital I2L ranging control integrated circuit designed for use with the Texas

　　Instruments TL852 sonar ranging receiver integrated circuit.

　　The TL851 is designed for distance measurement from six inches to 35 feet. The device has an internal oscillator

　　that uses a low-cost external ceramic resonator. With a simple interface and a 420-kHz ceramic resonator， the

　　device will drive a 50-kHz electrostatic transducer.

　　The device cycle begins when Initiate （INIT） is taken to the high logic level. There must be at least 5 ms from

　　initial power-up （VCC） to the first initiate signal in order for all the device internal latches to reset and for the

　　ceramic-resonator-controlled oscillator to stabilize. The device will transmit a burst of 16 pulses each time INIT

　　is taken high.

　　The oscillator output （OSC） is enabled by INIT. The oscillator frequency is the ceramic resonator frequency

　　divided by 8.5 for the first 16 cycles （during transmit） and then the oscillator frequency changes to the ceramic

　　resonator frequency divided by 4.5 for the remainder of the device cycle.

　　When used with an external 420-kHz ceramic resonator， the device internal blanking disables the receive input

　?。≧EC） for 3.8 ms after initiate to exclude false receive inputs that may be caused by transducer ringing. The

　　internal blanking feature also eliminates echos from objects closer than 1.3 feet from the transducer. If it is

　　necessary to detect objects closer than 1.3 feet， then the internal blanking may be shortened by taking the

　　blanking inhibit （BINH） high， enabling the receive input. The blanking input （BLNK） may be used to disable the

　　receive input and reset ECHO to a low logic level at any time during the device cycle for selective echo exclusion

　　or for a multiple-echo mode of operati