551 315 01
Service Channel (channel 0) (USB Node)
Registers in Service channel:
This constant holds the highest SWNo in the node, and a GUID for the entire device.
The purpose of this record is to be able to identify a connected device. The record includes registered manufacturer number, the type number of the device and a string identifying the manufacturer.
The record is of the following type:
This SWNo shows the nodeaddress of its neighbour. If the node is unable to obtain the NeighbourNodeAddress, this register will hold the value 254 and an actual data error will be set in the response.
By writing 255 to the Reset variable, the device will perform a reset, and ExternalReset in ChError will be set TRUE. Any other value than 255 can cause random behaviour.
This variable is a record of the following type:
The serial number is used for service purposes and acts as a 'key' for setting the P-NET address and number of masters for the P-NET node.
A special function is included for identifying a device connected to a network containing many other devices, having the same or unknown node addresses, and to enable a change of the node address and number of masters via the P-NET.
Setting a new node address and number of masters via P-NET, is performed by writing the required node address and number of masters, together with the serial number of the device in question, into the PNETSerialNo at node address 126 (calling all devices). All nodes on the P-NET will receive the message, but only the node in the device with the transmitted serial number will store the node address and the number of masters.
An attempt to write data to node address 126 will give no reply. Consequently the calling master must disable the generation of a transmission error when addressing this node.
In the device, the SerialNo = "XXXXXXXXPD", is set by PROCES-DATA, and cannot be changed. The eight “X”es indicate the serial number, and PD is the initials of PROCES-DATA.
FreeRunTimer is a timer to which internal events are synchronized. The timer is of type LongInteger in 1/256 Second.
This variable is a record having the following structure:
This variable holds the net parameters Baudrate, ErrorCheck and NoOfMasters for the port used to access the variable. For example, if the variable is accessed from port 1, the net parameters for port 1 are accessed. The variable can’t be accessed from Process-Pascal.
The variable is stored in memory type EEPROM RPW, meaning it can only be changed if WriteEnable is True.
Baudrate holds the bit rate for the port from which the variable is accessed. Which values are legal depends on the type of the port.
ErrorCheck holds the errorcheck method used for the port from which the variable is accessed. False means “Default (1 byte) errorcheck”, and True means “Extended (2 byte) errorcheck”.
The value of NoOfMasters can be from 0 to 32 but no requests will be sent on P-NET while NoOfMasters = 0.
This register defines the maximum number of retries made in the event of a transmission error, before the error is reported. The defined maximum number of retries is for each block in a LONG LOAD / STORE. Therefore, the value of Retries should be very low.
RegNo 13: WriteEnable
Write protected variables can only be changed when WriteEnable is TRUE. After reset, WriteEnable is set to FALSE.
Each channel type is identified by means of a unique GUID. The value of GUID for the Service channel is: PD/551315-01.
There are two sets of error bits, actual and historical. The actual error bits reflect the current situation and will automatically follow any change.
The historical error bits reflect past situations and have the job of holding sporadic errors. The historical error bits are set together with the corresponding actual bits. They remain set after a read, so each individual bit must be cleared by setting it to FALSE. Only the bits where the corresponding actual bit is FALSE can be cleared.
The “His data error” bit in the P-NET response is set if any historical bit is TRUE.
The “Act data error” bit in the P-NET response reflects the validity of the data in the response. Overload, electrical error or an error in other registers involved in calculating the result gives “Act data error”.