28 Issue Number: 3
TELEGRAM 2
The second telegram from the master also indicates a READ cycle, but
the stamp number is now 2. The data byte would contain the parameter
number for the parameter that is to read.
Bit b15-b12 b11-b8 b7-b4 b3-b0
Value 1XXX 0010 0000 0010
Data word = 0x8202 Stamp number = 2 Parameter = 2
When the second telegram has been received and processed in the
slave node, it is mirrored in the non-cyclic IN word. This is the signal to
the master controller program that the second telegram of the message
has been received and understood, and the third telegram can be
transmitted.
TELEGRAM 3
The third telegram from the master acts as the indication to the slave
node to send the data high byte from the requested parameter. The
data byte is not used in this telegram, and should be set to 0.
Bit b15-b12 b11-b8 b7-b4 b3-b0
Value 1XXX 0011 XXXX XXXX
Data word = 0x8300 Stamp number = 3 Data high byte = XX
When the third telegram has been received and processed in the slave
node, the node will mirror the stamp number in the non-cyclic IN word,
and load the high byte of the parameter value into the data byte.
Bit b15-b12 b11-b8 b7-b4 b3-b0
Value 10XX 0011 0000 0101
Data word = 0x8305 Stamp number = 3 Data high byte = 0x05
If an invalid parameter was specified in telegrams 1 and 2, e.g.
parameter is write only, or does not exist, the Profibus-DP interface will
set the ERROR bit to 1 (b14 = 1). The data bits will have no
significance.
Bit b15-b12 b11-b8 b7-b4 b3-b0
Value 11XX 0010 XXXX XXXX
Data word = 0xC200 Stamp number = 2
If an error is reported, it is recommended that the non-cyclic data word
is set to 0 to ensure that the non-cyclic state machine is completely
reset, and ready for the next non-cyclic READ or WRITE sequence.
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