Atmel SpW-10X user manual Setting the SpaceWire port transmit data rate, Txrate +1

SpW-10X	Ref.:	UoD_SpW-10X_
SpaceWire Router		UserManual
	Issue:	3.4
User Manual
	Date:	11th July 2008

Vdd	3.3 V
2850 Ω	2850 Ω	20 kΩ
91 µA	87 µA		12 µA	3.05 V
	10 mV		RT =100 Ω
			99 µA 3.04 V

16 kΩ

190 µA

+

‐

Figure 8-3 Deactivated LDVS driver output connected to external bias network on LVDS input

Current can now flow from the 3.3 volt supply to ground. When the bias resistors for 10mV noise margin are used, the total current flowing out of the LVDS outputs is around 200 µA as illustrated in Figure 8-3

WARNING

The deactivate mode (see also section 9.4.3) does not tri-state the LVDS outputs. The LVDS outputs are cold-sparing and when disabled both outputs in an LVDS differential pair are pulled up to 3.3V and have an impedance of the order of 1 kohm. Since they are differential outputs and are both are at the same voltage no current will flow. If, however, external noise bias resistors are being used then a small current (around 200 µA, 0.7 mW power) can flow. This is substantially less than the normal operating current of LVDS outputs and hence saves power.

8.1.6 Setting the SpaceWire port transmit data rate

The SpaceWire port transmit data rate is dependent on the input signal FEEDBDIV (See section 5.1), the PLL output clock divider value TXDIV (See section 9.5.9) and the data rate divider value TXRATE in each SpaceWire link control register (See section 9.4.3). The resultant data rate is determined by the function.

⎛	⎛	(100MHz + (20MHz * FEEDBDIV ))⎞ ⎞
⎜	⎜		⎟ ⎟
		2TXDIV +1
DataRate = ⎜	⎝		⎠ ⎟		* 2
		TXRATE +1		⎟
⎜
⎜				⎟
⎝				⎠

The output of the PLL is also used to provide the 10 Mbits/s transmit clock used during SpaceWire link initialisation.

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