B&B Electronics 1939STB manual RS-232 Baud Change, Baud Rate Setup

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	Byte	Byte 3			Byte 4		Byte 5	Byte 6	Byte 7
1	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.

1939STB4600 Manual 9

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