Vaisala PTB200 User Manual download pdf (Page 7)

PTB 200 6 (28)

Digital Barometers

SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1

2.4 Serial output mode connections

The serial communication can take place either using RS 232C or TTL

level signals. In both cases the barometer is connected to the host

system with three wires (TX, GND, RX) (see Figure 4). No handshaking

lines are used.

GND

RS 232C TTL TTL INVERT

Fig. 4 Serial bus connections and jumpers

The selection between the RS 232C and TTL level output signals is

made with a jumper (see Fig. 4). The TTL level output signal has two

phase alternatives: TTL and TTL INVERT. The TTL output is in phase

with the TXD line of the Intel 8051 microprocessor and the TTL INVERT

output is in phase with the RS 232C output.

Although the PTB 200 barometers use a single polarity supply, both

positive and negative voltage levels occur in the output in the RS 232C

output mode. The higher the supply voltage, the higher are the output

voltages in the transmission line of the barometer; for example, at 12

VDC supply voltage the output voltage levels are approximately ± 8

VDC. The TTL level output voltages are 0 and 5 VDC.

If the supply voltage is raised and the baud rate lowered, the RS 232C

interface can be used over far longer distances than specified for the

standard RS 232C interface.

The receiving RX line accepts both RS 232C and TTL level voltages as

input; the TTL level phase selection does not affect the receiving line of

the barometer.

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Vaisala PTB200 User Manual Page 7