RS-232

RS-232 supports point-to-point communications between one base (usually the data logger) and one external device. See RS-232 single-ended full-duplex communications. Data bits are sent from the base to external devices across the transmit (Tx) line with respect to DC ground. The Tx line idle state is between –25 V and –3 V, depending on the transmitter. The transition from negative voltage to above 3 V begins data transmission.

NOTE:

Most RS-232 devices are also compatible with the data logger using TTL-inverted communications.

NOTE:

The data logger uses about -7 V to represent logic 1, and about 5.8 V to represent logic 0.


(Click image to expand/collapse display)

RS-232 Tx voltage with respect to GND

RS-485/RS-422

RS-485 and RS-422 support communications between 32 base and 32 external devices. See RS-485 differential-pair half-duplex communications and RS-485/RS-422 differential-pair full-duplex communications. Differential voltage between two lines (A & B) transmit data. When the voltage of B with respect to A is between -0.2 V and -5 V that is interpreted as logic 0. When the differential voltage in the range of positive 0.2 V to 5 V that is interpreted as logic 1.

NOTE:

The CR350 uses about -1 V to represent logic 0, and about 1 V to represent logic 1.


(Click image to expand/collapse display)

RS-485 Voltage B with respect to A

TTL

TTL supports point-to-point communications between one base and one external device. See RS-232 single-ended full-duplex communications. Data bits are sent from base to external device with a voltage between transmit (Tx) and ground. The transmit line idle state is 5 V (logic 1). Data is sent after one clock cycle once the voltage is pulled low (to 0 V).


(Click image to expand/collapse display)

TTL Tx voltage with respect to GND

TTL-Inverted

The only difference between TTL-inverted and TTL is that the logic is inverted. The idle state for TTL-inverted is 0 V instead of 5 V. See RS-232 single-ended full-duplex communications. Data is sent after the voltage is pulled high (to 5 V).

NOTE:

Many RS-232 devices are compatible with this communications protocol.


(Click image to expand/collapse display)

TTL-inverted Tx voltage with respect to GND