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1939STB4600 Manual 9
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91 792444 – Fax +353 91 792445
RS-232 Baud Change
Setting byte-3/nibble-2 to 2 and byte-4/nibble-1 to 2 causes the 1939STB
to change baud. This function also requires 3 bytes of additional information
bytes 5, 6, and 7. It is important to note that after a baud change the PC must
have its baud changed to match the baud of the 1939STB for communication
to exist. If communication is lost after a baud change and cannot be
recovered, disconnecting the 1939STB from its power source will restore the
1939STB to its default baud rate of 9600 baud, 1 stop bit, 8 data bits, no
parity.
Table 11. Baud Rate Setup
Byte 3 Byte 4 Byte 5 Byte 6 Byte 7 Byte
1
Byte
2
Nibble 2 Nibble 1 Nibble 2 Nibble 1 UB3 Baud 1 Baud 2
81 21 0010 0011 0000 0010
81 21 23 hex 02 hex 03 hex 00 hex 06 hex
Table 11 shows how an internal command is used to set the 1939STB to a
baud rate of 300, 1 stop bit, 8 data words, and no parity. Byte 3 nibble 2 sets
the internal command function. A nibble value of 2 sets the J1939STB into
the Internal Function mode. Nibble 1 of byte 3 tells the 1939STB 3 bytes will
follow Byte 4. Byte 4, nibble 1 is set to 2 telling the 1939STB to perform a
baud change using the information contained in bytes 5, 6, and 7.
Table 12. Baud Rate Setup
Baud Rate Decimal Divisor Hex Divisor MSB (Baud 2) Hex Divisor LSB (Baud 1)
300 1556 06 hex 00 hex
1200 384 01 hex 80 hex
2400 192 00 hex C0 hex
9600 48 00 hex * 30 hex *
19200 24 00 hex 18 hex
38,400 12 00 hex 0C hex
57,600 8 00 hex 08 hex
* Setup default value.