PLC & Control

Siemens data frame is not usual, open your port with: speed 9600 baud data 8 bits stop 1 bit parity EVEN DLE (10hex) is a control character, used to inform the receiver that the following char is to be considered a control character and not a data byte. In other words, DLE is a software switch within the AS511 protocol to divide control and data bytes. Whenever a DATA byte containing the value 10hex is to be sent, the sender must DOUBLE the char. This means that to send a data byte 10hex, the sender must send 10hex 10hex (DLE DLE). The receiver must consider the thing, so a single DLE will mean a protocol signal, while two consecutive DLE are to be interpreted as a SINGLE data byte containing the 10hex value. This is a little tricky, since the receiver NEVER knows exactly how many bytes to expect. Take also note that the AG can answer DLE NAK instead of DLE ACK if the requested operation can not be carried out. In this case, the PG must abort the communication and wait for 500ms before attempting a new communication. The value of 500mS is also applied as timeout value in case of missing response from the partner.This also means that no "holes" of 500mS (or more) are allowed during a communication (e.g. within a DB_READ function) To read or write a datablock value, you need to know its address in PLC memory. Therefore you must invoke B_INFO function to know the address, then you can call DB_READ or DB_WRITE by giving the initial and final address of the area to be read or written. Be aware that in SIMATIC the LSB/MSB bytes order is reversed:

SIMATIC:

15..............0

BYTE 0 BYTE 1

INTEL:

15..............0

BYTE 1 BYTE 0

To obtain the correct integer value of a dataword, the user must therefore: - swap the received bytes and - swap the bytes before sending them to the PLC B_INFO input: block number output: initial address of DW0 in AG PG AS (hex) (hex) ---------------------- function start -------- 02 ----> STX <---- 10 DLE <---- 06 ACK 1A ----> B_INFO function code = 1Ah <---- 02 STX 10 ----> DLE 06 ----> ACK <---- 16 AG answer=16h <---- 10 DLE <---- 03 ETX 10 ----> DLE 06 ----> ACK ---------------------- header info -------- 01 ----> ID=01h for Datablock XX ----> DB number (0..255) 10 ----> DLE 04 ----> EOT <---- 10 DLE <---- 06 ACK ---------------------- data -------- <---- 02 STX 10 ----> DLE 06 ----> ACK <---- 00 NUL <---- XX DB initial address <---- XX <---- 70 synchronization code: 70 70 <---- 70 <---- 41 block ID and DB number : 41 XX <---- XX <---- XX PG ID code: XX XX <---- XX <---- XX library number: XX XX <---- XX <---- XX block length (words): XX XX <---- XX <---- 10 DLE <---- 03 ETX 10 ----> DLE 06 ----> ACK ---------------------- terminate -------- <---- 02 STX 10 ----> DLE 06 ----> ACK <---- 12 AG "end of transmission" code: 12h <---- 10 DLE <---- 03 ETX 10 ----> DLE 06 ----> ACK DB_READ input: initial address in AG final address in AG output: contents of datawords PG AS (hex) (hex) ---------------------- function start -------- 02 ----> STX <---- 10 DLE <---- 06 ACK 04 ----> DB_READ function code = 04h <---- 02 STX 10 ----> DLE 06 ----> ACK <---- 16 AG answer=16h <---- 10 DLE <---- 03 ETX 10 ----> DLE 06 ----> ACK ---------------------- header info -------- XX ----> initial address in AG: XX XX XX ----> XX ----> final address in AG: XX XX XX ----> 10 ----> DLE 04 ----> EOT <---- 10 DLE <---- 06 ACK ---------------------- data -------- <---- 02 STX 10 ----> DLE 06 ----> ACK <---- 00 NUL <---- 00 NUL <---- 00 NUL <---- 00 NUL <---- 00 NUL <---- XX first byte of data <---- XX <---- XX . . . . . . <---- XX <---- XX <---- XX last byte of data <---- 10 DLE <---- 03 ETX 10 ----> DLE 06 ----> ACK ---------------------- terminate -------- <---- 02 STX 10 ----> DLE 06 ----> ACK <---- 12 AG "end of transmission" code: 12h <---- 10 DLE <---- 03 ETX 10 ----> DLE 06 ----> ACK DB_WRITE input: - initial address in AG - contents of datawords output: - none PG AS (hex) (hex) ---------------------- function start -------- 02 ----> STX <---- 10 DLE <---- 06 ACK 03 ----> DB_WRITE function code = 03h <---- 02 STX 10 ----> DLE 06 ----> ACK <---- 16 AG answer=16h <---- 10 DLE <---- 03 ETX 10 ----> DLE 06 ----> ACK ---------------------- header info -------- XX ----> initial address in AG: XX XX XX ----> ---------------------- data -------- XX ----> first byte of data XX ----> XX ----> . . . . . . XX ----> XX ----> XX ----> last byte of data 10 ----> DLE 04 ----> EOT ----> 10 DLE ----> 06 ACK ---------------------- terminate -------- <---- 02 STX 10 ----> DLE 06 ----> ACK <---- 12 AG "end of transmission" code: 12h <---- 10 DLE <---- 03 ETX 10 ----> DLE 06 ----> ACK

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