Serial Communications Protocol Specifications - Swissvacuum.com

The entire task can be described as follows:
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Fig. 2 Communication overview
MASTER (PC) SLAVE (CHAMBER CONTROLLER)
Prepare query to send
Send query to the slave via serial line.
Wait answer from the Slave
The Modbus protocol implemented in the MicroPLC chamber controller is the binary type (also known as RTU). In
RTU mode data are sent as 8 bits binaries characters. A remote control computer (typically a PC) is always the
master device meanwhile the MicroPLC controller is the slave device.
ERROR DETECTION
As well known, communication errors can occour during data transmission on a serial line. The errors generally come
from noise on the line and electrical or hardware problems on the devices used for the communication.
The software that controls the communication (the PC) takes care to identify the errors and manage them with
appropriate actions.
Specifically, when an error is detected, the data packet must be discarded (not used) because the data inside are
probably corrupted and meaningless.
Only when no error is present, the data packet can be decoded to extract the answer coming from the chamber
controller.
The errors can be present in both sides of the serial line (PC side and chamber controller side). If the error is identified
by the chamber controller, then no answer will be send to the master.
Fig. 3 Noise on the line
Wait data from the master
Decode packet and prepare the
answer
Send packet to the master
Serial communications protocol vers. 2.02 Angelantoni Industrie Spa Massa Martana (PG) Italy