PROFIBUS INTERFACE
71
5
5.5.4 Example
4:
Fragmentation of Commands
For this example, the Master will send a CBx “Write Tag Data” command to the Slave (the
RFID Controller) to write 50 bytes to a tag.
We will assume for this example that the both the input and output buffers have been
configured to 32 bytes each. This means that the command itself cannot completely fit in the
output buffer, and therefore needs to be sent in fragments. Long Tag writes that exceed the
buffer size can be separated into multiple writes, with each write addressed to a different
location of the tag, but if it is desirable to send one long CBx command, it can be
accomplished using this method of fragmentation:
Sending the command:
In
Byte 2
of the output buffer the Master places the length (in bytes) of the data packet (first
Fragment of the CBx Command) we are sending – in this case the first fragment will be 28
bytes – the maximum size of a packet when the output buffer is 32 bytes.
(The entire CBx command we are planning to send, over 3 fragments, is 62 bytes).
In
Byte 3
through
Byte 30
the Master places the first 28 bytes of this CBx command.
(See the
Green
changes below)
Output Buffer
Input Buffer
Byte # Value
Byte # Value
00:
80
Output Buffer Control Byte
(OBCB)
7 6 5 4 3 2 1 0
[1] [0] [0] [0] [0] [0] [0] [0]
00
80
Input Buffer Control Byte
(IBCB)
7 6 5 4 3 2 1 0
[1] [0] [0] [0] [0] [0] [0] [0]
01: 00 (Always
0)
01: 00
02:
1C
(Packet length in bytes)
02: 00
03:
04:
05:
06:
07:
08:
09:
10:
11:
12:
13:
14:
15:
16:
17:
18:
19:
20:
21:
22:
23:
24:
25:
26:
27:
28:
29:
30:
00
1F
AA
06
00
01
03
E8
00
00
00
32
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
(CBx Command word length MSB)
(CBx Command word length LSB)
(CBx Command Type)
Always AA
(CBx Command Opcode)
0x06 = Write Tag Data
(CBx Command, byte not used)
(CBx Command “Node ID”)
(CBx Command Timeout MSB)
(CBx Command Timeout LSB)
0xE8 = 1000 ms timeout
(CBx Command Start Address MSB)
(CBx Command Start Address LSB)
address 0
(CBx Command Length MSB)
(CBx Command Length LSB)
50 bytes
(CBx Command Data Byte 1)
(CBx Command Data Byte 2)
(CBx Command Data Byte 3)
(CBx Command Data Byte 4)
(CBx Command Data Byte 5)
(CBx Command Data Byte 6)
(CBx Command Data Byte 7)
(CBx Command Data Byte 8)
(CBx Command Data Byte 9)
(CBx Command Data Byte 10)
(CBx Command Data Byte 11)
(CBx Command Data Byte 12)
(CBx Command Data Byte 13)
(CBx Command Data Byte 14)
(CBx Command Data Byte 15)
(CBx Command Data Byte 16)
03:
04:
05:
06:
07:
08:
09:
10:
11:
12:
13:
14:
15:
16:
17:
18:
19:
20:
..
30:
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
..
00
31: 80
Data Consistency Byte (OBDCB)
31: 80
Data Consistency Byte (IBDCB)
Summary of Contents for GWY-01-PBS-01
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