RS-485 Timeout Selection | B&B Electronics FOSTCDR instruction

the driver could be disabled before transmission is complete, resulting in data corruption. If the time is set too long, the RS-485 device may respond before the RS-422/485 driver in the FOSTCDR is disabled, corrupting this response. We recommend that the timeout be set for approximately one character time or longer. The character times for several different baud rates are selectable on switch positions 1 through 5. If you need a different timeout than what is provided, R10 can be removed and replaced with a different value R9. Table 1 shows the different timeout values for the switch positions as well as some typical R9 replacement values.

Table 1: RS-485 Timeout Selection

Baud Rate	Pos. 1	Pos. 2	Pos. 3	Pos. 4	Pos. 5	R9	Time(ms)
1200	ON	OFF	OFF	OFF	OFF	820 KΩ	8.20

2400	ON	OFF	OFF	OFF	OFF	430 KΩ	4.30

4800	OFF	OFF	OFF	OFF	ON	Not Used	2.20

9600	OFF	OFF	OFF	ON	OFF	Not Used	1.30

19.2K	OFF	OFF	ON	OFF	OFF	Not Used	0.56

38.4K	OFF	ON	OFF	OFF	OFF	Not Used	0.27

57.6K	ON	OFF	OFF	OFF	OFF	Not Used	0.22

76.8K	ON	OFF	ON	ON	OFF	Not Used	0.14

115.2K	ON	ON	ON	OFF	OFF	Not Used	0.10

153.6K	ON	OFF	OFF	OFF	OFF	6.2 KΩ	0.06

230.4K	ON	OFF	OFF	OFF	OFF	4.3 KΩ	0.04

460.8K	ON	OFF	OFF	OFF	OFF	2.2 KΩ	0.02

Position 6 of SW1 sets the unit as a “Repeating” module or a “Terminating” module. When the FOSTCDR is set as a “Repeating” module, data arriving on the Fiber Optic receiver is repeated back out the transmitter. When set as a “Terminating” module, data arriving at the Fiber optic receiver is not sent back out the Fiber Optic transmitter. Position 6 must be turned “On” when the FOSTCDR is to be used as one of the Slaves in a multi-drop ring configuration. It must be turned “Off” when the FOSTCDR is to be used as the Master in a multi-drop configuration or as either end of a point to point communication line. See Figure 3 for typical system setups using the FOSTCDR in its different modes.

4	FOSTCDR2999 Manual

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