DP83953 datasheet(30/90 Pages) NSC

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4.0 Functional Description (Continued)

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4.7 Description Of Hardware Connection For Pro-

cessor And Display Interface

Display Update Cycles

The RIC2A possesses control logic and interface pins

which may be used to provide status information concern-

ing activity on the attached network segments and the cur-

rent status of repeater functions. These status cycles are

completely autonomous and require only simple support

circuitry to produce the data in a form suitable for a light

emitting diode "LED" display. The display may be used in

one of two modes:

1. Minimum mode - General Repeater Status LEDs

2. Maximum mode - Individual Port Status LEDs

Minimum mode, intended for simple LED displays, makes

available four status indicators. The first LED denotes

whether the RIC2A has been forced to activate its jabber

protect functions. The remaining 3 LEDs indicate if any of

the RIC2A's network segments are: (1) experiencing a col-

lision, (2) receiving data, (3) currently partitioned. When

minimum display mode is selected the only external com-

ponents required are a 74LS374 type latch, the LEDs and

their current limiting resistors.

Maximum mode differs from minimum mode by providing

display information specific to individual network segments.

This information denotes the collision activity, packet

reception and partition status of each segment. In the case

of 10BASE-T segments the link integrity status and polarity

of the received data are also made available. The wide

variety of information available in maximum mode may be

used in its entirety or in part. This allows the system

designer to choose the appropriate complexity of status

display commensurate with the specification of the end

equipment.

The signals provided and their timing relationships have

been designed to interface directly with 74LS259 type

addressable latches. The number of latches used being

depend upon the complexity of the display. Since the

latches are octal, a pair is needed to display each type of

segment specific data (13 ports means 13 latch bits). The

accompanying Table 2 and Table 3 show the function of the

interface pins in minimum and maximum modes. Table 4

shows the location of each port's status information when

maximum mode is selected. This may be compared with

the connection diagram Figure 12.

Immediately following the Mode Load Operation (when the

MLOAD pin transitions to a high logic state), the display

logic performs an LED test operation. This operation lasts

one second. While it is in effect, all of the utilized LEDs will

blink on. Thus, an installation engineer is able to test the

operation of the display by forcing the RIC2A into a reset

cycle (MLOAD forced low). The rising edge on the MLOAD

pin starts the LED test cycle. During the LED test cycle

the RIC2A does not perform packet repetition opera-

tions.

The status display possesses a capability to lengthen the

time an LED is active. At the end of the repetition of a

packet, the display is frozen showing the current activity.

This freezing lasts for 30 milliseconds or until a subsequent

packet is repeated. Thus at low levels of packet activity, the

display stretches activity information to make it discernible

to the human eye. At high traffic rates the relative bright-

ness of the LEDs indicates those segments with high or

low activity.

It should be mentioned that when the Real Time Interrupt

(RTI) occurs, the display update cycle will stop and after

RTI is serviced, the display update cycle will resume activ-

ity.

Table 2. Status Display Pin Functions in Minimum Mode

Signal Pin Name

Function in MINIMUM MODE

No operation

Provides status information indicating if there is a collision occurring on one of the segments

attached to this RIC2A.

Provides status information indicating if one of this RIC2A's ports is receiving a data or collision

packet from a segment attached to this RIC2A.

Provides status information indicating that the RIC2A has experienced a jabber protect condi-

tion.

Provides Status information indicating if one of the RIC2A's segments is partitioned.

D(7:5)

No operation

STR0

This signal is the latch enable for the 374 type latch.

STR1

This signal is held at a logic one.

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