Manual

ALTOSONIC V
ModBus Manual 0300 rev07 E 7.30855.35.00 Page 57 of 64
9 Appendices
9.1 Appendix A: Time out values
The character length lies between 9 and 12 bits
The UFP-V determines the time between two bytes to recognise a communication failure or the end of
a message. UFP-V discriminates between a timeout between 2 bytes and a timeout after the last byte,
which occurs at the end of a message.
The time between two bytes is measured with a resolution of ±100 us.
To detect the timeout state (end of message) a timer is incremented every millisecond. A received byte
will reset the timer. Every millisecond the timer value will be checked for a timeout value, when it will
exceed a defined value it will mark the last received byte as end of message.
Notice that the serial communication is a asynchrony process with respect to the used timer interrupt,
therefore a ‘jitter’ of 1 ms must be taken into account.
Modbus defined timeout values for every baud rate with N number of bytes:
Baud
rate
9 bit 10 bit 11 bit 12 bit
Timeout
chars
3.5 4.0 3.5 4.0 3.5 4.0 3.5 4.0
1200 26.25 ms 30 ms 29.17 ms 33.34 ms 32.08 ms 36.67 ms 35.00 ms 40 ms
2400 13.16 ms 15 ms 14.58 ms 6.67 ms 16.04 ms 18.33 ms 17.50 ms 20 ms
4800 6.56 ms 7.5 ms 7.29 ms 8.33 ms 8.02 ms 9.17 ms 8.75 ms 10 ms
9600 3.28 ms 3.75 ms 3.65 ms 4.16 ms 4.01 ms 4.58 ms 4.38 ms 5 ms
19200 1.64 ms 1.88 ms 1.82 ms 2.08 ms 2.01 ms 2.29 ms 2.19 ms 2.5 ms
The maximum time to detect a timeout (end of message) used in UFP-V:
Baud rate 9 10 11 12
1200 28…29 ms 31…32 ms 33…34 ms 36…37 ms
2400 14…15 ms 15…16 ms 16…17 ms 18…19 ms
4800 6…7 ms 7…8 ms 8…9 ms 9…10 ms
9600 3…4 ms 3…4 ms 4…5 ms 4…5 ms
19200 2…3 ms 2…3 ms 2…3 ms 2…3 ms
The maximum time between 2 characters in a message (GAP) used in UFP-V:
Baud rate 9 10 11 12
1200 28.2 ms 31.3 ms 34.4 ms 37.5 ms
2400 14.1 ms 15.6 ms 17.2 ms 8.8 ms
4800 7.0 ms 7.8 ms 8.6 ms 9.4 ms
9600 3.5 ms 3.9 ms 4.3 ms 4.7 ms
19200 1.8 ms 1.95 ms 2.2 ms 2.4 ms