GE RSTi-EP User Manual page 218

Data Transfer
The process data length can be parameterized to be 8 or 16 Bytes. Byte 0 is used for status and
diagnosis, Byte 1 for the data segment length, and the remaining 6 or 14 Bytes are user data.
Process input data: The data sent from the serial device are written into the receive memory of the
UR20 module. As soon as the SPS request results in that RX_CNT is not equal RX_CNT_ACK, the data
will be sent in segments via the fieldbus coupler to the PLC. The successfully data transfer will be
acknowledged to the module.
The receive memory can safe a maximum of 255 Bytes. A software handshake (XON/XOFF) or a
hardware handshake (RTS/CTS) can be parameterised using the flow control, so that an alarm will
warn against a buffer overflow.
Process output data: The data sent from the PLC via the fieldbus coupler are written into the
transmission memory of the UR20 module. The module is continously checking whether data are
ready to be sent or a data transfer to the device has been finished successfully. Not till then the next
data will be transferred.
Byte Format
IB0 Word
IB1 Word
IB 2 ... IB 7
or
IB 2 ... IB 15
GFK-2958E
Process Input Data EP-5261
Name Bit
IX0.0
IX0.1
IX0.2
IX0.3
Status and
Diagnosis
IX0.4
IX0.5
IX0.6
IX0.7
Length of the
data segment
/ of the
subsequent
diagnosis data
Received data
RSTi-EP User Manual
Chapter 5 Detailed Descriptions of I/O Modules
Description Remarks
RX = 0: Receive memory is empty
Data in the receive
RX = 1: A telegramm or telegramm
memory
segment in the receive memory is
ready for transmission.
Only 10 characters are left in the
Receive memory
receive memory. XOFF will be set if
nearly full
parametrerised.
Not used
The RX_CNT value is assigned to each
data segment of the process input
RX_CNT
data while transmission. The sequence
or the RX_CNT values is:
Binary: 00, 01, 10, 11, 00, ...
Decimal: 0, 1, 2, 3, 0, ...
RX_CNT
A faulty data seqence indicates
missing data segments.
The TX_CNT_ACK value is a copy of the
TX_CNT_ACK
TX_CNT value, which has been
transferred together with the last data
segment of the process output data.
TX_CNT_ACK
TX_CNT_ACK acknowledges that the
data has been taken over successfully.
STAT = 1: Communication with the
device is without fault.
STAT
STAT = 0: Faulty communication with
the device.
Length of the data / diagnosis data in
RX
this frame
User data of the
transferred telegram
segment
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