Mitel NWK954 manual LED Drivers, Polarity selection on BPDOEN, BPDIEN and BPCOLOEN

NWK954

The IRD bus in each hub is connected to the 5-bit backplane bus via a bidirectional buffer. This allows data to be driven from any hub to all other hubs in the stack. The bidirectional buffer is controlled by 2 control signals (BPDOE_N and BPDIE_N) which can be taken from any one of the NWK954 devices in the hub. BPDOE_N and BPDIE_N default to being active low but can be independently changed to active high by the addition of an external pull-down resistor, as shown in Fig.7. This resistor is sensed during RESET_N = 0.

Data transfers on the backplane are synchronous to the backplane clock. The backplane clock is supplied by whichever hub supplies the data. When receiving data from the backplane, the backplane clock is enabled onto the local BPCLK signal by BPDIE_N. BPCLK connects to all NWK954s in the hub. When a hub supplies data to the backplane, BPCLK is driven locally and is enabled onto the backplane by BPDOE_N.

Each hub in a stack indicates receive activity on any of its twisted pair ports by asserting the backplane activity output (BPACTOUT_N). BPACTOUT_N can be taken from any one of the NWK954s and drives one of the backplane activity signals via an external buffer. The backplane supports up to 8 backplane activity signals. The backplane activity signals from up to 7 other hubs connect to the local BPACTIN_N signals which are input to all NWK954s in the hub.

When a collision occurs between 2 twisted pair ports in a hub, the event is communicated to other stacked hubs by BPCOL_N which is enabled onto the backplane collision signal by BPCOLOE_N. BPCOLOE_N defaults to being active low but can be changed to active high by the addition of an external pull-down resistor. This resistor is sensed during RESET_N=0. BPCOL_N is also asserted when a collision occurs between two twisted pair ports on different hubs. Collision events are cormmunicated to all hubs through the BPCOLIN_N signal which connects to all NWK954s in the hub.

LED Drivers

The NWK954 provides 2 LED drivers per port to indicate port status (RXLED_N and ERLED_N), one LED driver to indicate collisions (COLLED_N) and 5 LED drivers to indicate network utilization (ACTLED_N). The LED drivers pull the output pins low to turn the LEDs on. The LEDs are turned on or off for a minimum of 40ms to ensure observability.

The port status LEDs indicate a variety of conditions and provide rapid diagnosis of network faults,as shown in Table 1. The network utilization LEDs are turned on at the thresholds given in Table 2.

NWK954

Enable signal configured for active low operation

NWK954

1 0 k

Enable signal configured for active high operation

Fig. 7 Polarity selection on BPDOE_N, BPDIE_N and

BPCOLOE_N

RXLED_N	ERLED_N	Port status
Off	Off	No incoming signal
Off	Flash	Incoming signal but no idle pattern recognized*
On	Off	Link established, no incoming data packets
Flash	Off	Link established, receiving data packets
On	On	Link established, but port partitioned due to excessive collisions
		or port isolated due to false carriers
		or port disabled due to jabber
Flash off	Flash on	Link established, false carrier or invalid data detected

*In 802.3 a continuous signal of the required amplitude is sufficient to establish a link but no data can be passed to the repeater controller until the descrambler has locked on to an idle pattern.

	Table 1
LED	Network utilization
ACTLED_N0	>1%
ACTLED_N1	>12·5%
ACTLED_N2	>25%
ACTLED_N3	>50%
ACTLED_N4	>60%
	Table 2

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