D300529 0115 - BL67 I/O modules
12-21
BL67-1RS485/422
Process output data
The data received from the PLC are loaded into the 64-bit transmit-buffer in the module.
The transmission is realized in a 8-byte fo
rmat which is structured as follows:
1 control byte is required to ensure trouble-
free transmission of the data.
1 byte contains, signals to start the flushing of
transmit- and receive buffer.
6 bytes are used to contain the user data.
Byte Byte
DP/PN
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
n = offset of output data; depending on extension of station and the corresponding fieldbus.
Control byte
n
n + 7
STATRES RX_CNT_ACK TX_CNT TX_BYTE_CNT
Flushing of receive- or transmit-buffer
n + 1
n + 6
reserved TXBufDis
RXBUF
FLUSH
TXBUF
FLUSH
Data bytes
n + 2
n + 5
TX_data byte 0
n + 3 n + 4
TX_data byte 1
n + 4 n + 3
TX_data byte 2
n + 5 n + 2
TX_data byte 3
n + 6 n + 1
TX_data byte 4
n + 7 n
TX_data byte 5
Table 12-2:
Process output
da
ta
Designation Value Description
TX_BYTE_CNT 0 - 7 Number of the valid bytes
in this data segment.
TX_CNT 0 - 3 This value is transferred together with every data segment. The
TX_CNT values are sequential:
00 → 01 → 10 → 11 → 00…
(de
cimal: 0 → 1 → 2 → 3 → 0…)
Er
rors in this sequence show the loss of data segments.
RX_CNT_ACK 0 - 3 The value TX_CNT_ACK is a copy of the value TX_CNT. The value
RX_CNT was transferred together with the last data segment of the
process input data.
The value TX_CNT_ACK is a confirmation of successful acceptance
of the data segment using TX_CNT.
STATRES 0 - 1 This bit is set to reset the STAT bit in the process input data.
With the change from 1 to 0 the STAT bit is reset (from 0 to 1). The
clearing of the receive and transmit buffer by RXBUF FLUSH/TXBUF
FLUSH is possible.
If this bit is 0, all changes in TX_BYTE_CNT, TX_CNT and
RX_CNT_ACK are ignored. The value 1.0 or the transition from 0 to
1 disables the clearing of the receive and transmit buffer by the
RXBUF FLUSH/TXBUF FLUSH.
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