294 MAINTENANCE AND LUBRICATION Note: The tachometer output and speedometer output are 50% duty cycle, Transistor-Transistor Logic (TTL) compatible, square wave signals that are calibrated to provide a standard pulse rate of 12 pulses per engine revolution for the tachometer output and 30,000 pulses per mile for the speedometer output. TTL compatibility of these outputs may be affected by other devices connected to these outputs. Tachometer (RPM) Output This terminal is to be used for devices requiring information for engine speed signals. (See the Warning and Note above.) Speedometer (MPH) Output This terminal is to be used for devices requiring information for vehicle speed signals. (See the Warning and Note above.) SAE/ATA J1708 Posts (Serial Links A and B) This is a serial communication interface. It conforms to the SAE/ATA J1708 Recommended Practice for Serial Data Communications Between Microcomputer Systems in Heavy-Duty Vehicle Applications. (See the Warning above.) CB Radio Power Jack The CB radio power jacks are located on the dashboard of the day cab, and on the headliner of the sleeper. Power Jack (+) This is a 12-volt, switched battery connection. It is to be used to power the vehicle’s CB radio. It is protected by a 15-amp circuit breaker and will supply power when the key is in the ACCESSORY position or ON position. Power Jack (-) This is a ground connection. It is to be used as a power return connection for the vehicle’s CB radio.
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