5. Each Component Function
User’s Manual
55
Terminal Resistor when RS-485 is in Use
Set with JP4 inside the top cover. The factory setting is " terminal
resistor not available."
1 and 2 shorted
Receiver terminal
resistor available
2 and 3 shorted
Receiver terminal
resistor not available
123
123
Figure 5.2. Terminal Resistor Settings
Control of Transmitted Data in Half-Duplex Mode
In half-duplex mode, the transmission buffer needs to be controlled
in order to prevent collision of transmitted data. The BOX-PC
uses RTS and controls the buffer with modem control register's bit 1.
Transmission and reception gate control by the register setting of
port address 4006h and 4007h is allowed only for the RS-422/485
(Serial port D). For more information see section, "General-
purpose I/O and Remote Reset" in Chapter 5.
Modem control register
(Set I/O address +4H) bit 1: 0 … RTS is High.
(Disable transmission)
1 … RTS is Low.
(Enable transmission)
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