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GIO Hardware and Software Configuration

GIO Board Unit Number

Up to a maximum of eight (8) GIOs or Guidance Slave Boards (GSBs) can be theoretically interfaced to a Guidance Controller.  Therefore, this section describes how to configure and address up to 8 GIO or GSB boards.  However, due to communication timing and 24VDC power considerations, which are described below, a maximum combination of four (4) GIOs or GSBs is a more practical limit except for special system configurations.

GIOs and GSBs can be connected to the RS-485 daisy chain in any order without altering their operation or identification. A GIO or GSB is not identified by a unit number that is embedded in its low-level communication messages. This unit number is specified by jumpers on the GIO. A GIO's unit number is automatically combined with "GIO_" to generate a keyword that is used to configure the communication protocol between the GIO and its master controller. The unit number can be arbitrary selected and does not need to be sequentially assigned, but each GIO or GSB must have a unique unit number within a given RS-485 system. 

The setting of the GIO's Unit Number Jumpers is presented in Table 18-1 along with the corresponding unit number and keyword identifier.

NOTE: The Unit Number Jumpers for the GIO are J7/J8/J9, whereas the GSB utilizes J8/J9/J10.

RS-485 Signal Termination

There is one hardware configuration option that is dependent upon the ordering of modules in the RS-485 daisy chain. For noise immunity, termination jumpers must be installed on the GIOs, GSBs, or controller on the extreme ends of the RS-485 daisy chain. The termination jumpers must be removed for all controllers or boards in between. On the GIO board, the Termination Jumper is labeled J6. Consult the hardware description for a specific master controller to determine its RS-485 termination jumper location.

Controller Software Configuration

For the controller to communicate with an IO module, the GIO's GIO_Keyword must be entered into the "Servo network node identifier" (DataID 151) parameter database array in the master controller. This provides the controller with the information required to communicate with the GIO board. The position of the GIO_Keyword in the DataID 151 array assigns the board a "network node number." Within the controller's software environment, the network node number (and not the GIO's unit number) is used to reference DIO on the GIO board. By convention, the first network node is always the master controller and the first element of the DataID 151 is always the controller's serial number.

For example, if the GIO Unit Number Jumpers are set to select unit #4 (Keyword GIO_4), to define the GIO as the second network node, DataID 151 should be defined as follows:

DataID 151: "<master>," "GIO_4", "", "", "", "", . . .

Normally, only elements at the end of the DataID 151 array can be blank and a blank entry cannot precede any non-blank servo node entry. As a special case, blank entries may occur before a GIO keyword. So the user could enter DataID 151 as follows:

DataID 151: "<master>", "", "", "", "", "GIO_4"

This allows GIO boards to be assigned to fixed node numbers regardless of how many other slave boards might be in the system. Having a fixed node number means the I/O signal numbers are also fixed.

24VDC Logic Power Considerations

The GIO must be provided with 24VDC to power both the board's logic and to drive the input and output signals. The amount of 24VDC power available for GIO boards may limit the number of boards that can be wired in a system.

As a wiring convenience, GIOs and GSBs typically draw the 24VDC power from the same 10-pin daisy chained ribbon cable that provides the RS-485 signals. In this configuration, the Guidance Controller and its associated 24VDC power supply provide the logic and signal power to the GIOs and GSBs.

As of 2013, all Guidance Controllers can output a maximum of 2A at 24VDC on the 10-pin RS-485 connector assuming that the controller's 24VDC power supply has sufficient power. Prior to 2013, this was limited to only 1.35A.

The minimum power requirement for the GIO's logic is 0.05A. In the worst case, where a board's digital outputs are all configured as sourcing and are driving 100mA and the digital inputs are configured as sourcing as well, a single GIO could draw 1.05A or more. Even with 2A available from the controller, at most, two (2) GIOs could be supported by the power available from a controller.

Fortunately, in a typical system, even if the GIO's digital outputs are configured as sourcing, 20mA to 50mA of drive per channel is more common. The user can expect a typical GIO configured with sourcing outputs to draw 0.5A, which permits up to four (4) GIOs to be interfaced to a single controller.

If GSBs are interfaced as well, their power consumption must be taken into account as well as any motor power that is drawn from the controller's 24VDC via the RS-485 cable.

If the controller's available power on the RS-485 cable is not sufficient for an application, an external 24VDC power source can be wired to the GIO and GSB boards (although this is not as convenient) or the digital signals could be configured as sinking if practical.

Communication Timing Considerations

Each GSB exchanges messages with the master controller every motion control trajectory cycle. The trajectory period is determined by the parameter "Trajectory Generator update period in sec" (DataID 600) on the master controller. This parameter typically ranges from 1-4 msec and determines the delay in reading or writing input and output values on the GIO.

As the number of GIO and/or GSB boards increases, the trajectory period must also be increased in order to accommodate the increased transmission times. Table 18-2 shows the maximum number of GSB or GIO nodes possible for different trajectory periods.