is monitored by means of a timeout (ADT = acknowledgement delay time). To establish this time, the delays on the transmission line as well as in the serial receiver are of interest.
After the data block is sent by the software of the master to the serial driver, the following delays must be added for the dimensioning of ADT for a serial direct connection:
ADT = serial transfer time of data block + serial transfer time of data block + processing time at the slave
Example:
Length of data block: 100 bytes
Length of acknowledgment: 1 byte
Serial data rate: 9600 baud, no parity, 1 start bit, 8 data bits, 1 stop bit = ~ 1 ms / byte
Processing time at serial terminal device: 2msMinimum ADT: (100 bytes + 1 byte) + 2ms = ~103ms
If a serial master and slave are linked over the network and a Com-Server, the transfer time of typically 4 to 7ms for communication in both directions (option "network delay" = 0) that is required by the Com-Server, must be added to the above value. In addition, delays within the network must also be taken into account. If the following conditions are met, a typical value of approx. 1 to 2 ms can be assumed:
- Network load < 30%
- No ARP address resolution, i.e. existing TCP connection
- no load-disconnecting components (switches, routers, etc.)
Compared with the above described example of a serial direct connection, the combination of network and Com-Server would result in a typical additional delay of approx. 10-18ms:
(2 x 4-7ms for Com-Server) + (2 x 1-2ms for Netzwerk)
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