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How UOS uses the comm port control signals RTS, CTS, DTR and DSR. Also, the difference between serial communications modes Direct, Radio and Modem.

Summary
UOS has three serial communication modes: Direct, Radio and Modem. Mode selection is located at the channel level of the UOS PowerTool. Select the channel by clicking on the channel icon Channel Icon. The Mode field is located in the Primary Channel area of the screen.
Direct Specifies a direct cable connection (RS-232, RS-422, RS-485, Leased Lines). Direct mode uses Channel level port control settings (RTS, CTS, DSR and DTR) and Device level RTS Keyup, RTS Keydown and RTS Turnaround settings to control message flow to the process hardware.
Radio Specifies a radio transmission. Selecting Radio mode is for user information only. UOS operation is the same as Direct mode.
Telephone Specifies communications by a telephone modem. You must enter the telephone number in the Device Primary Telephone Number field. UOS dials the number entered in this field when it polls for data unless a connection with the device has already been established.
Telephone mode also uses Channel level port control settings (RTS, CTS, DSR and DTR) and Device level RTS Keyup,RTS Keydown and RTS Turnaround settings to control message flow to the process hardware.
You should set up your NT system for TAPI if you plan to use a telephone modem.
 
UOS RTS Control Fields
The RTS control fields (RTS Keyup, RTS Keydown and RTS Turnaround) are UOS PowerTool device level settings. This means that they apply to a field device and can be set differently for each device. To view or modify the fields, select a device by clicking on the device icon Device Icon in the UOS PowerTool connection tree. The RTS control fields are located in the Primary Radio Setup area of the screen.
RTS control fields can be used two ways.
a) To control message flow with no hardware interaction.
b) To control message flow with hardware interaction.
Option a) can be used if a device cannot respond to a second request for data immediately following transmission of data to UOS. In this case you could set RTS Turnaround to the time period that the device needs to recover. UOS would receive data and then wait for the time period before sending the next data request message.
Option b) can be used for RS-485 communications to switch the tri-state comm lines between transmit and receive. However, a better option is to use a good RS-232 to RS-485 converter that uses data-sense to switch the comm lines. The converter will switch faster than software RTS control resulting in less garbled data. In some cases software RTS control of the comm lines will not work at all. Option b) can also be used for radio and modem control.
Important Note: The UOS PowerTool device level RTS control field settings override the channel level RTS setting (RTS checkbox).: The UOS PowerTool device level RTS control field settings override the channel level RTS setting (RTS checkbox).
 

Radio Setup Parameter

Operation

RTS Keyup Specifies the length of time in milliseconds that UOS waits between raising the comm port RTS signal and sending a message to a device. The RTS control sequence is: 1) Raise comm port RTS signal 2) Wait the length of time specified in RTS Keyup 3) Send message.
RTS Keydown Specifies the length of time in milliseconds that UOS waits after sending a message to lower the comm port RTS line. The RTS control sequence is: 1) Send message, RTS is high at this point 2) Wait the length of time specified in RTS Keydown 3) Lower comm port RTS signal
RTS Turnaround Specifies the length of time in milliseconds that UOS waits between receiving a message and initiating another message to send.

The RTS control sequence is: 1) Receive a message 2) Wait the length of time specified in RTS Turnaround 3) Send another message according to RTS Keyup/RTS keydown settings.

 
UOS RTS, CTS, DSR and DTR Operation
The serial port control fields (RTS, CTS, DSR and DTR) are UOS PowerTool channel level settings. This means that the same setting applies to all devices connected to the selected comm port. To view or modify the fields, select a channel by clicking on the channel icon Channel Icon in the UOS PowerTool connection tree. The serial port control fields (check boxes) are located in the Primary Channel area of the screen.
The table below describes how UOS controls RTS and DTR and uses CTS and DSR.
 

Control

Operation

RTS The RTS signal is an output (controlled by UOS) from UOS.

If the RTS box is checked, the serial port RTS signal is raised high when UOS initializes the port (When the Start button is pressed). RTS will stay high ONLY if no value is entered into the Device level RTS Keyup or RTS Keydown fields. The Channel level Mode settings (Direct, Radio or Telephone) have no affect. If RTS Keyup or RTS Keydown is set to a specified value(s), the comm port RTS signal will go high on initialization and then behave according to the specified RTS Keyup/RTS Keydown value(s).

CTS The CTS (Clear To Send) signal is an input (controlled by the field device) to UOS.

If the CTS box is checked, UOS will not send a message to the device until the CTS signal goes high. UOS will receive messages independent of the state of the CTS signal.

DSR The DSR (Data Set Ready) signal is an input (controlled by the field device) to UOS.

If the DSR box is checked, UOS will not send a message to the device until the DSR signal goes high. UOS will receive messages independent of the state of the DSR signal.

The DSR signal usually indicates that the process hardware is powered up and ready.

DTR The DTR signal is an output (controlled by UOS) from UOS.

If the DTR box is checked, the serial port DTR signal is raised high when UOS initializes the port (Start button is pressed). DTR will remain high until UOS is stopped (Stop button is pressed). The settings for device level RTS Keyup or RTS Keydown or the Channel level Mode settings (Direct, Radio or Telephone) have NO effect on DTR operation.

The Data Terminal Ready (DTR) signal is normally used to enable a connection with the process hardware. Once connected, the DTR signal must remain asserted to maintain connection.

Telephone modems typically require the DTR signal set to high. Therefore, you may have to check this box if you are communicating using a telephone mode.

 

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