B |
Communications Protocol
This is the low level definition of the serial communications Protocol. A driver for the most commonly used portions of the protocol has already been written for C, and compiler Basic. This driver is contained in the MCROCOM.C file from the distribution diskette. Sample C programs which use this driver are provided. Refer to the MCROCOMM.C file and examples in the \COMM subdirectory of your disk.
DLE STX data1 data2 ... DLE ETX cc
DLE = 16
STX = 2
ETX = 3
data N ± Data byte. If the data is equal to DLE (16), two DLE bytes will be transmitted. Maximum of 255 data bytes (excluding DLE bytes that were inserted).
cc± Checksum byte. 2's complement of 8 bit sum of data bytes only (excluding DLE bytes that were inserted and the DLE/STX DLE/ETX).
Data Format
NOTES:
HAll addresses are in the range of 11 bits. Most significant 5 bits are 0s.
HBit values are packed into bytes (byte 0 bit 0, byte 0 bit 1, ..., byte 1 bit 0, etc.).
HAnalog values, addresses, and program words are 2 bytes each, MSB first.
HPLC id value is ignored by the programming port, but it shouldn't be dropped.
HProgram write can be done only when the PLC is in Program mode (stopped).
HWhen downloading a program in more than one block, the blocks must be in ascending address order.
Read Discretes
ID 01 count addr_high addr_low
Reply:
ID 01 count addr_high addr_low data1 data2 ...
ID | ± PLC ID number |
count | ± number of bits (discretes) to read |
addr_high | ± High byte of address of the first discrete to read |
addr_low | ± Low byte of address of the first discrete to read |
dataN | ± Data read |
Micro PLC Programmer's Guide ± Aptil 1994 |
